Revert "xds: fix TSAN data races in xDS security components and tests (#12829)" (#12840)

This reverts commit 6faedad93771cc7aa8da075d963969e2ce19a83a to address
the post-merge comments in PR #12829.

xds/src/main/java/io/grpc/xds/internal/security/DynamicSslContextProvider.java

diff --git a/xds/src/main/java/io/grpc/xds/internal/security/DynamicSslContextProvider.java b/xds/src/main/java/io/grpc/xds/internal/security/DynamicSslContextProvider.java
index 619c06b..e7b27cd 100644
--- a/xds/src/main/java/io/grpc/xds/internal/security/DynamicSslContextProvider.java
+++ b/xds/src/main/java/io/grpc/xds/internal/security/DynamicSslContextProvider.java
@@ -42,7 +42,7 @@
 
   protected final List<Callback> pendingCallbacks = new ArrayList<>();
   @Nullable protected final CertificateValidationContext staticCertificateValidationContext;
-  @Nullable protected volatile AbstractMap.SimpleImmutableEntry<SslContext, X509TrustManager>
+  @Nullable protected AbstractMap.SimpleImmutableEntry<SslContext, X509TrustManager>
       sslContextAndTrustManager;
 
   protected DynamicSslContextProvider(

xds/src/main/java/io/grpc/xds/internal/security/certprovider/CertProviderSslContextProvider.java

diff --git a/xds/src/main/java/io/grpc/xds/internal/security/certprovider/CertProviderSslContextProvider.java b/xds/src/main/java/io/grpc/xds/internal/security/certprovider/CertProviderSslContextProvider.java
index 948b6ce..cb99ca6 100644
--- a/xds/src/main/java/io/grpc/xds/internal/security/certprovider/CertProviderSslContextProvider.java
+++ b/xds/src/main/java/io/grpc/xds/internal/security/certprovider/CertProviderSslContextProvider.java
@@ -39,10 +39,10 @@
   @Nullable private final NoExceptionCloseable rootCertHandle;
   @Nullable private final CertificateProviderInstance certInstance;
   @Nullable protected final CertificateProviderInstance rootCertInstance;
-  @Nullable protected volatile PrivateKey savedKey;
-  @Nullable protected volatile List<X509Certificate> savedCertChain;
-  @Nullable protected volatile List<X509Certificate> savedTrustedRoots;
-  @Nullable protected volatile Map<String, List<X509Certificate>> savedSpiffeTrustMap;
+  @Nullable protected PrivateKey savedKey;
+  @Nullable protected List<X509Certificate> savedCertChain;
+  @Nullable protected List<X509Certificate> savedTrustedRoots;
+  @Nullable protected Map<String, List<X509Certificate>> savedSpiffeTrustMap;
   private final boolean isUsingSystemRootCerts;
 
   protected CertProviderSslContextProvider(

xds/src/main/java/io/grpc/xds/internal/security/certprovider/FileWatcherCertificateProviderProvider.java

diff --git a/xds/src/main/java/io/grpc/xds/internal/security/certprovider/FileWatcherCertificateProviderProvider.java b/xds/src/main/java/io/grpc/xds/internal/security/certprovider/FileWatcherCertificateProviderProvider.java
index 84e99de..e4871dc 100644
--- a/xds/src/main/java/io/grpc/xds/internal/security/certprovider/FileWatcherCertificateProviderProvider.java
+++ b/xds/src/main/java/io/grpc/xds/internal/security/certprovider/FileWatcherCertificateProviderProvider.java
@@ -38,9 +38,8 @@
 
   // TODO(lwge): Remove the old env var check once it's confirmed to be unused.
   @VisibleForTesting
-  public static volatile boolean enableSpiffe =
-      GrpcUtil.getFlag("GRPC_EXPERIMENTAL_SPIFFE_TRUST_BUNDLE_MAP", false)
-          || GrpcUtil.getFlag("GRPC_EXPERIMENTAL_XDS_MTLS_SPIFFE", false);
+  public static boolean enableSpiffe = GrpcUtil.getFlag("GRPC_EXPERIMENTAL_SPIFFE_TRUST_BUNDLE_MAP",
+      false) || GrpcUtil.getFlag("GRPC_EXPERIMENTAL_XDS_MTLS_SPIFFE", false);
   private static final String CERT_FILE_KEY = "certificate_file";
   private static final String KEY_FILE_KEY = "private_key_file";
   private static final String ROOT_FILE_KEY = "ca_certificate_file";

xds/src/main/java/io/grpc/xds/internal/security/trust/CertificateUtils.java

diff --git a/xds/src/main/java/io/grpc/xds/internal/security/trust/CertificateUtils.java b/xds/src/main/java/io/grpc/xds/internal/security/trust/CertificateUtils.java
index b595fe5..41a3980 100644
--- a/xds/src/main/java/io/grpc/xds/internal/security/trust/CertificateUtils.java
+++ b/xds/src/main/java/io/grpc/xds/internal/security/trust/CertificateUtils.java
@@ -30,7 +30,7 @@
  * Contains certificate utility method(s).
  */
 public final class CertificateUtils {
-  public static volatile boolean useChannelAuthorityIfNoSniApplicable
+  public static boolean useChannelAuthorityIfNoSniApplicable
       = GrpcUtil.getFlag("GRPC_USE_CHANNEL_AUTHORITY_IF_NO_SNI_APPLICABLE", false);
 
   /**