Always unlink the out_vdex_file.

Even if we pass the same vdex file as input and output to
dex2oat, make sure we unlink it if dex2oat failed.

bug:38113240
Test: manual, killing dex2oat invocation
Change-Id: I406014f97a2c3b2bd646e13b5d86dfa0eaa2692f