build:wafsamba: refactored the gcc-based dependency calculation

[github at samba.org]

New comment by ita1024 on Samba Github repository

https://github.com/samba-team/samba/pull/31#issuecomment-158123648
Comment:
The change you suggested is unnecessary:
1. The removal of `buildtools/wafsamba/gccdeps.py` went missing after the pull request was updated, so the old `gccdeps.py` file was still present, causing errors in the build.
2. For extra safety, the stale `gccdeps.pyc` is now removed before it is picked up in the configuration so that the first build will not raise any error.