Utils: Remove FilePath::isWritablePath() uses

And fix remaining users.

Change-Id: I41c27908f2e9f1e253d0b51830ba351b29a84ec5
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/libs/utils/filepath.h

@@ -94,7 +94,6 @@ public:
     bool needsDevice() const;
     bool exists() const;
 
-    bool isWritablePath() const { return isWritableDir(); } // Remove.
     bool isWritableDir() const;
     bool isWritableFile() const;
     bool ensureWritableDir() const;