stop removing completion results caching flag from parse options

It seems to cause more harm than good.

Not sure to understand if there is any downside to this change,
hopefully time will tell.

Related issues:

- #326
- #332

server/src/TUManager.cpp

@@ -36,11 +36,6 @@ TUManager::TUManager()
   parseTUOptions_ |= CXTranslationUnit_IncludeBriefCommentsInCodeCompletion;
 #endif
 
-  // XXX: Completion results caching doesn't seem to work right, changes at the
-  // top of the file (i.e: new declarations) aren't detected and do not appear
-  // in completion results.
-  parseTUOptions_ &= ~CXTranslationUnit_CacheCompletionResults;
-
   // XXX: A bug in old version of Clang (at least '3.1-8') caused the completion
   // to fail on the standard library types when
   // CXTranslationUnit_PrecompiledPreamble is used. We disable this option for