Revert rL359778 : [clangd] Fix code completion of macros defined in the...

Revert rL359778 : [clangd] Fix code completion of macros defined in the preamble region of the main file.

Summary:
This is a tricky case (we baked the assumption that symbols come from
the preamble xor mainfile pretty deeply) and the fix is a bit of a hack:
We look at the code to guess the macro names, and deserialize them from
the preamble "by hand".

Reviewers: ilya-biryukov

Subscribers: ioeric, MaskRay, jkorous, arphaman, kadircet, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D60937
........
Fix buildbots http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-ubuntu-fast/builds/47684/

llvm-svn: 359796