Remove strip.sh intermediates

The intermediate files generated by strip.sh --keep-symbols can be
very large, and are not useful after the build.  Remove them once
the final output file has been generated.

Saves ~6GB on an aosp_sailfish-userdebug build.

Test: m checkbuild
Change-Id: I0413f16ac5f423bc1b010cc9b8538f19bdea561e