Revert "[Serialization] Fix some Clang-tidy modernize and Include What You Use...

Revert "[Serialization] Fix some Clang-tidy modernize and Include What You Use warnings; other minor fixes (NFC)."

This reverts commit r330068. It breaks the lldb bots due to assertion
failures (more details on cfe-commits).

http://lab.llvm.org:8080/green/view/LLDB/job/lldb-cmake/
http://lab.llvm.org:8080/green/view/LLDB/job/lldb-cmake/6341/

stderr: Assertion failed: (M && "imported decl from no module file"), function loadPendingDeclChain, file /Users/vsk/src/llvm.org-lldbsan/llvm/tools/clang/lib/Serialization/ASTReaderDecl.cpp, line 3861.
llvm-svn: 330080