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/languageclient/client.h

@@ -195,10 +195,6 @@ public:
     void log(const LanguageServerProtocol::ResponseError<Error> &responseError) const
     { log(responseError.toString()); }
 
-#ifdef WITH_TESTS
-    void forceHighlightingOnEmptyDelta();
-#endif
-
 signals:
     void initialized(const LanguageServerProtocol::ServerCapabilities &capabilities);
     void capabilitiesChanged(const DynamicCapabilities &capabilities);