The command deletes all files under $GOPATH/pkg/gomobile dir
that keeps downloaded files and precompiled objects during the
last gomobile init run.
'gomobile clean' will be suggested in case of gomobile init
failures due to downloaded file hash mismatch.
For golang/go#15973
Change-Id: Ie9d3cfa7aef9d68931fd68f7b58d1a18c9d4b3b8
Reviewed-on: https://go-review.googlesource.com/24074
Reviewed-by: David Crawshaw <crawshaw@golang.org>
