Cleanup srandmember implementation

Simplified implementation to use Array#sample, which does more of the
heavy lifting for us.

Change-Id: Ie4e8adbb7fb0af6b332ef16558fa5ebd28999d38
Reviewed-on: https://gerrit.causes.com/33203
Reviewed-by: Shane da Silva <shane@causes.com>
Tested-by: Shane da Silva <shane@causes.com>