[ctxprof][nfc] Drop Section in writeFlatSection (#130654)

It matches `writeContextual`, and also, it's not the whole section that's being written there, just a profile, piecemeal.

Author: mtrofin

llvm/include/llvm/ProfileData/PGOCtxProfWriter.h

@@ -88,8 +88,8 @@ class PGOCtxProfileWriter final : public ctx_profile::ProfileWriter {
   void endContextSection() override;
 
   void startFlatSection();
-  void writeFlatSection(ctx_profile::GUID Guid, const uint64_t *Buffer,
-                        size_t BufferSize);
+  void writeFlat(ctx_profile::GUID Guid, const uint64_t *Buffer,
+                 size_t BufferSize);
   void endFlatSection();
 
   // constants used in writing which a reader may find useful.

llvm/lib/ProfileData/PGOCtxProfWriter.cpp

@@ -126,9 +126,8 @@ void PGOCtxProfileWriter::writeContextual(const ContextNode &RootNode) {
   writeImpl(std::nullopt, RootNode);
 }
 
-void PGOCtxProfileWriter::writeFlatSection(ctx_profile::GUID Guid,
-                                           const uint64_t *Buffer,
-                                           size_t Size) {
+void PGOCtxProfileWriter::writeFlat(ctx_profile::GUID Guid,
+                                    const uint64_t *Buffer, size_t Size) {
   Writer.EnterSubblock(PGOCtxProfileBlockIDs::FlatProfileBlockID, CodeLen);
   writeGuid(Guid);
   writeCounters({Buffer, Size});
@@ -240,7 +239,7 @@ Error llvm::createCtxProfFromYAML(StringRef Profile, raw_ostream &Out) {
   if (!SPR.FlatProfiles.empty()) {
     Writer.startFlatSection();
     for (const auto &[Guid, Counters] : SPR.FlatProfiles)
-      Writer.writeFlatSection(Guid, Counters.data(), Counters.size());
+      Writer.writeFlat(Guid, Counters.data(), Counters.size());
     Writer.endFlatSection();
   }
   if (EC)