Utils: Remove unused FileName::chop

It's unused, and non-const, so not nice-to-have in the url-using case.

Change-Id: I5ec7d06e74b20b22a2fd8467222a135a6dcce814
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/utils/fileutils.h

@@ -95,7 +95,6 @@ public:
     FileName &appendString(const QString &str);
     FileName &appendString(QChar str);
 
-    using QString::chop;
     using QString::clear;
     using QString::count;
     using QString::isEmpty;