Delete jmod workDir

Files in this directory aren't exposed to the rest of the build, so
deleting them saves some space. The `jmod create` command was also
producing non-deterministic files, which are not relevant because
they're not used anywhere else, but it makes it easier to find
non-determinism that matters if we delete them.

Test: Presubmits
Change-Id: I5d57826b438368f24a7a2a7ab1ccd6c16f240124