Revert "Clang support for -flto=thin." (bot failures)

Rolling this back for now since there are a couple of bot failures on
the new tests I added, and I won't have a chance to look at them in detail
until later this afternoon. I think the new tests need some restrictions on
having the gold plugin available.

This reverts commit r250398.

llvm-svn: 250402
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 61144fc..4220487 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -499,9 +499,7 @@
 
   Opts.MergeFunctions = Args.hasArg(OPT_fmerge_functions);
 
-  Opts.PrepareForLTO = Args.hasArg(OPT_flto, OPT_flto_EQ);
-  const Arg *A = Args.getLastArg(OPT_flto, OPT_flto_EQ);
-  Opts.EmitFunctionSummary = A && A->containsValue("thin");
+  Opts.PrepareForLTO = Args.hasArg(OPT_flto);
 
   Opts.MSVolatile = Args.hasArg(OPT_fms_volatile);