Disable -disable-concrete-type-metadata-mangled-name-accessors flag.

With the improvements to protocol casting performance from swiftlang#33487, the demangling overhead is
hopefully manageable for most people using this flag today.

Author: jckarter

lib/Frontend/CompilerInvocation.cpp

@@ -1448,9 +1448,6 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
   if (Args.hasArg(OPT_disable_debugger_shadow_copies))
     Opts.DisableDebuggerShadowCopies = true;
 
-  if (Args.hasArg(OPT_disable_concrete_type_metadata_mangled_name_accessors))
-    Opts.DisableConcreteTypeMetadataMangledNameAccessors = true;
-
   if (Args.hasArg(OPT_use_jit)) {
     Opts.UseJIT = true;
     if (const Arg *A = Args.getLastArg(OPT_dump_jit)) {

test/IRGen/access_type_metadata_by_mangled_name.swift

@@ -1,8 +1,4 @@
 // RUN: %target-swift-frontend -emit-ir -parse-stdlib %s | %FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-%target-endian
-// RUN: %target-swift-frontend -emit-ir -disable-concrete-type-metadata-mangled-name-accessors -parse-stdlib %s | %FileCheck %s --check-prefix=DISABLED
-
-// DISABLED-NOT: __swift_instantiateConcreteTypeFromMangledName
-// DISABLED-NOT: MD" = {{.*}} global
 
 // CHECK: @"$s36access_type_metadata_by_mangled_name3FooCyAA3BarCyAA3ZimCyAA4ZangCGGGMD" = linkonce_odr hidden global { i32, i32 }