CppTools: Call ProjectInfo::finish when we get it

No need to require the project managers to do this. Also, it is easy to
forget.

Change-Id: I96f7a5e5547418678af9653e5753c372f0880e5a
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/clangcodemodel/test/clangcodecompletion_test.cpp

@@ -623,7 +623,6 @@ CppTools::ProjectInfo createProjectInfo(ProjectExplorer::Project *project,
     const CppTools::ProjectPart::Ptr projectPart = createProjectPart(files, defines);
     ProjectInfo projectInfo = ProjectInfo(project);
     projectInfo.appendProjectPart(projectPart);
-    projectInfo.finish();
     return projectInfo;
 }