Merge branch 'cc/test-oidmap'

Extend the test coverage a bit.

* cc/test-oidmap:
t0016: add 'remove' subcommand test
test-oidmap: remove 'add' subcommand
test-hashmap: remove 'hash' command
oidmap: use sha1hash() instead of static hash() function
t: add t0016-oidmap.sh
t/helper: add test-oidmap.c