Remove toolbox's obsolete 'wipe' command.

It hasn't worked in some time (it removes /data/dalvik-cache, which is
required by art), and if you're prepared to reboot (to let init put back
all the directories a working system needs) there are other ways to wipe
data (such as "fastboot format userdata reboot").

Bug: 19644330
Change-Id: Ib074ea21cc28409a506d66d75060bb4ad85539e2