Clang: Remove project tracking on clangbackend side

...as it is not needed. Just provide the compilation arguments as part
of the Document.

As a side effect, re-initializing the backend after a crash is cheaper
and will not freeze the UI anymore (referenced bug).

Task-number: QTCREATORBUG-21097
Change-Id: I866e25ef1fd5e4d318df16612a7564469e6baa11
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/tools/clangbackend/source/clangbackendclangipc-source.pri

@@ -50,8 +50,6 @@ HEADERS += \
     $$PWD/diagnosticsetiterator.h \
     $$PWD/fixit.h \
     $$PWD/fulltokeninfo.h \
-    $$PWD/projectpart.h \
-    $$PWD/projects.h \
     $$PWD/skippedsourceranges.h \
     $$PWD/sourcelocation.h \
     $$PWD/sourcerange.h \
@@ -106,8 +104,6 @@ SOURCES += \
     $$PWD/diagnosticset.cpp \
     $$PWD/fixit.cpp \
     $$PWD/fulltokeninfo.cpp \
-    $$PWD/projectpart.cpp \
-    $$PWD/projects.cpp \
     $$PWD/skippedsourceranges.cpp \
     $$PWD/sourcelocation.cpp \
     $$PWD/sourcerange.cpp \