pro2cmake: Fix reported make flake8 issues

pro2cmake.py:458:5: F841 local variable 'is_parent_path' is assigned
to but never used

Pick-to: 6.2
Change-Id: I1c61efe5cf568fa0c99b07eed28b93d3444a5fac
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>

util/cmake/pro2cmake.py

@@ -455,7 +455,6 @@ def process_qrc_file(
 
     # Small not very thorough check to see if this a shared qrc resource
     # pattern is mostly used by the tests.
-    is_parent_path = dir_name.startswith("..")
     if not os.path.isfile(filepath):
         raise RuntimeError(f"Invalid file path given to process_qrc_file: {filepath}")