ClangRefactoring: Remove not used pch files

Because we use UUID for pch files every time we rebuild a pch we get
a new file. This patch is collecting and removing this pch files.

Change-Id: Ia8688e7215ee7b41f39b2285323eaa345056bda3
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/clangsupport/filesysteminterface.h

@@ -36,6 +36,7 @@ class FileSystemInterface
 public:
     virtual FilePathIds directoryEntries(const QString &directoryPath) const = 0;
     virtual long long lastModified(FilePathId filePathId) const = 0;
+    virtual void remove(const FilePathIds &filePathIds) = 0;
 
 protected:
     ~FileSystemInterface() = default;