[NFC][clang] Refactor getCompilationPhases()+Types.def step 2.

- Removing a few of the entries in the Flags for the Types.def table.
- Removing redundant parts of getCompilationPhases().

Flags have been removed from Types.def:

 a - The type should only be assembled: Now, check that Phases contains
     phases::Assemble but not phases::Compile or phases::Backend.
 p - The type should only be precompiled: Now, check that Phases contains
     phases::Precompile but that Flags does not contain 'm'.
 m - Precompiling this type produces a module file: Now, check that
     isPrepeocessedModuleType.



Differential Revision: https://reviews.llvm.org/D65176

llvm-svn: 367063