Remove clangsupport dependency from plugins

Change-Id: Ifd4215a590d32cd04fab720d0d8d5e746e81c6e8
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangcodemodel/test/clangbatchfileprocessor.cpp

@@ -55,7 +55,6 @@
 #include <QString>
 #include <QThread>
 
-using namespace ClangBackEnd;
 using namespace ProjectExplorer;
 
 namespace ClangCodeModel {