go/internal/gccgoimporter: remove temporary directories in test

Backport of https://golang.org/cl/164862.

Updates https://gcc.gnu.org/PR89406

Change-Id: Ic091d32c8f61d1d4e24161a256f69a659e900a2e
Reviewed-on: https://go-review.googlesource.com/c/164863
Reviewed-by: Than McIntosh <thanm@google.com>
1 file changed