LanguageClient: Re-highlight also on empty deltas

This is needed for e.g. ClangdClient, which may need to update even if
the highlighting delta from the server is empty.

Task-number: QTCREATORBUG-26183
Change-Id: I38398c9563fa7a6a1906c5cb57fd1cbcd444cbd9
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangcodemodel/test/clangdtests.cpp

@@ -1432,7 +1432,6 @@ ClangdTestCompletion::ClangdTestCompletion()
 void ClangdTestCompletion::initTestCase()
 {
     ClangdTest::initTestCase();
-    client()->forceHighlightingOnEmptyDelta();
     startCollectingHighlightingInfo();
 }