CPackRPM: Unset temporary component variables before re-use

Improve the fix from commit v2.8.9~136^2 (CPackRPM: avoid leakage of RPM
directive from one component to another, 2012-06-05) to clean up more
temporary variables.

Reviewed-by: Domen Vrankar <domen.vrankar@gmail.com>
Merge topic 'CPackRPM-cleanup-component-vars' into next

51a60973 CPackRPM: Unset temporary component variables before re-use