build:wafsamba: Removed the custom parse_flag override from the Samba scripts

[github at samba.org]

New comment by obnoxxx on Samba Github repository

https://github.com/samba-team/samba/pull/30#issuecomment-152735019
Comment:
Looks except  for one request:
Could you split this into two patches:
* 1st patch to third_party/waf to apply the upstream change
* 2nd patch to wafsamba to remove the now unneeded special treatment

Thanks - Michael