Clang: Create preamble on first parse

...now that parsing and creating the preamble is faster due to the
skipped function bodies.

As a consequence, we can remove all the extra jobs that were needed to
get an initial AST faster.

Change-Id: I79a66b8a0e8a180850af6daf353d9a679089bbb1
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/tools/clangbackend/source/clangcodemodelserver.cpp

@@ -481,7 +481,6 @@ void ClangCodeModelServer::processInitialJobsForDocuments(const std::vector<Docu
         DocumentProcessor processor = documentProcessors().processor(document);
         processor.addJob(JobRequest::Type::UpdateDocumentAnnotations);
         processor.addJob(JobRequest::Type::UpdateExtraDocumentAnnotations);
-        processor.addJob(JobRequest::Type::CreateInitialDocumentPreamble);
         processor.process();
     }
 }