Revert "make -fmodules-codegen and -fmodules-debuginfo work also with PCHs"

This caused PR44953. See also the discussion on D74846.

This reverts commit cbc9d22e49b434b6ceb2eb94b67079d02e0a7b74.
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 091bf56..362d3ea 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -502,12 +502,8 @@
 }
 
 void ASTDeclReader::ReadFunctionDefinition(FunctionDecl *FD) {
-  if (Record.readInt()) {
+  if (Record.readInt())
     Reader.DefinitionSource[FD] = Loc.F->Kind == ModuleKind::MK_MainFile;
-    if (Reader.getContext().getLangOpts().BuildingPCHWithObjectFile &&
-        Reader.DeclIsFromPCHWithObjectFile(FD))
-      Reader.DefinitionSource[FD] = true;
-  }
   if (auto *CD = dyn_cast<CXXConstructorDecl>(FD)) {
     CD->setNumCtorInitializers(Record.readInt());
     if (CD->getNumCtorInitializers())
@@ -1422,12 +1418,8 @@
       Reader.getContext().setBlockVarCopyInit(VD, CopyExpr, Record.readInt());
   }
 
-  if (VD->getStorageDuration() == SD_Static && Record.readInt()) {
+  if (VD->getStorageDuration() == SD_Static && Record.readInt())
     Reader.DefinitionSource[VD] = Loc.F->Kind == ModuleKind::MK_MainFile;
-    if (Reader.getContext().getLangOpts().BuildingPCHWithObjectFile &&
-        Reader.DeclIsFromPCHWithObjectFile(VD))
-      Reader.DefinitionSource[VD] = true;
-  }
 
   enum VarKind {
     VarNotTemplate = 0, VarTemplate, StaticDataMemberSpecialization
@@ -1686,12 +1678,8 @@
   Data.ODRHash = Record.readInt();
   Data.HasODRHash = true;
 
-  if (Record.readInt()) {
+  if (Record.readInt())
     Reader.DefinitionSource[D] = Loc.F->Kind == ModuleKind::MK_MainFile;
-    if (Reader.getContext().getLangOpts().BuildingPCHWithObjectFile &&
-        Reader.DeclIsFromPCHWithObjectFile(D))
-      Reader.DefinitionSource[D] = true;
-  }
 
   Data.NumBases = Record.readInt();
   if (Data.NumBases)