Clang: Do not show diagnostic category in inline annotations and issues pane

For build system diagnostics they are not displayed either.

Also, the error/warning is already encoded in the icon and the color.

However, the category is still shown in the tooltip.

Change-Id: I190ab17691c32786cefc20d058010c65cda5ace9
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangcodemodel/clangdiagnosticmanager.cpp

@@ -345,7 +345,7 @@ static void addTask(const ClangBackEnd::DiagnosticContainer &diagnostic, bool is
     }
 
     TaskHub::addTask(Task(taskType,
-                          diagnostic.text.toString(),
+                          Utils::diagnosticCategoryPrefixRemoved(diagnostic.text.toString()),
                           FileName::fromString(diagnostic.location.filePath.toString()),
                           diagnostic.location.line,
                           Constants::TASK_CATEGORY_DIAGNOSTICS,