oe/patch.py: Remove series file during Clean()

oe/patch.py: Remove series file during Clean()

Currently if there is a failed do_patch the series files get appended
so if there were two patches

a.patch
b.patch
and b.patch failed during next run it would append a.patch again
a.patch
b.patch
a.patch

and this would keep growing.

We can remove series file in Clean() because we populate it in Import()
anyway

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Acked-by: Chris Larson <chris_larson@mentor.com>
Acked-by: Eric Bénard <eric@eukrea.com>