[fuchsia GN] Don't use zxcpp

zxcpp is deprecated and superfluous with static libc++.

Bug: ZX-1751 #comment Removed boringssl users of zxcpp
Test: CQ
Change-Id: I5fb147ec5fa236c8d7ef4551c072208c073bbc41
diff --git a/BUILD.gn b/BUILD.gn
index 18ab020..6a9db32 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -45,7 +45,7 @@
   }
   configs += [ ":internal_config" ]
   if (is_fuchsia) {
-    deps = [ "//zircon/public/lib/zxcpp" ]
+    configs += [ "//build/config/fuchsia:static_cpp_standard_library" ]
   } else {
     configs += [ ":host_config" ]
   }
@@ -60,7 +60,7 @@
     ":crypto",
   ]
   if (is_fuchsia) {
-    deps += [ "//zircon/public/lib/zxcpp" ]
+    configs += [ "//build/config/fuchsia:static_cpp_standard_library" ]
   }
 }