Revert "[scudo] Enable standalone scudo."

This reverts commit 685ed0b7293290be0b505b798a6842c592e26b6e.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> [scudo] Enable standalone scudo.
> Test: None
> 
> Changes default for entire stack to scudo. Disables toolchain
> based mechanism.
> 
> Change-Id: I10317c7ad1eb4715101d12eb9dd0d11fc17a7a73

TBR=kostyak@google.com,davemoore@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I82b29e3dde8905fc1c2fef941f9da68ba80b69e9
diff --git a/build/config/scudo/scudo.gni b/build/config/scudo/scudo.gni
index 028d247..93d0a56 100644
--- a/build/config/scudo/scudo.gni
+++ b/build/config/scudo/scudo.gni
@@ -7,7 +7,7 @@
   # default (DNO-442)
   # Enable the [Scudo](https://llvm.org/docs/ScudoHardenedAllocator.html)
   # memory allocator.
-  use_scudo = false
+  use_scudo = true
 
   # Default [Scudo](https://llvm.org/docs/ScudoHardenedAllocator.html)
   # options (before the `SCUDO_OPTIONS` environment variable is read at
diff --git a/zircon/third_party/ulib/musl/BUILD.gn b/zircon/third_party/ulib/musl/BUILD.gn
index 7a89fb9..d664811 100644
--- a/zircon/third_party/ulib/musl/BUILD.gn
+++ b/zircon/third_party/ulib/musl/BUILD.gn
@@ -3,7 +3,7 @@
 # found in the LICENSE file.
 
 declare_args() {
-  malloc = "scudo"
+  malloc = "jemalloc"
 }
 
 config("headers") {