purge-locales: further refactoring after removing man paths

Since the man paths have been removed, it is no longer necessary to
grep them out and the loop can be simplified.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>