[ProfileData] Remove unused and racy FunctionSamples::Format after D51643

The write may be racy if ThinLTO creates multiple `InProcessThinBackend` instances.

llvm/include/llvm/ProfileData/SampleProf.h

@@ -1056,8 +1056,6 @@ public:
 
   void setContext(const SampleContext &FContext) { Context = FContext; }
 
-  static SampleProfileFormat Format;
-
   /// Whether the profile uses MD5 to represent string.
   static bool UseMD5;
 

llvm/lib/ProfileData/SampleProf.cpp

@@ -43,7 +43,6 @@ cl::opt<bool> GenerateMergedBaseProfiles(
 
 namespace llvm {
 namespace sampleprof {
-SampleProfileFormat FunctionSamples::Format;
 bool FunctionSamples::ProfileIsProbeBased = false;
 bool FunctionSamples::ProfileIsCSFlat = false;
 bool FunctionSamples::ProfileIsCSNested = false;

llvm/lib/ProfileData/SampleProfReader.cpp

@@ -1882,7 +1882,6 @@ SampleProfileReader::create(std::unique_ptr<MemoryBuffer> &B, LLVMContext &C,
     Reader->Remapper = std::move(ReaderOrErr.get());
   }
 
-  FunctionSamples::Format = Reader->getFormat();
   if (std::error_code EC = Reader->readHeader()) {
     return EC;
   }