Revert "Finish implementation of must_be decorator"

Russblau reported that something broke with this and
prevented his bot from editing. Reverting until we can
debug and figure out what went wrong.

This reverts commit 650ea9d2c319d5a58b708c87ad9048ad84491240.

Change-Id: I80dd97a75b909f9d2db2485f3681af444ebcd9b9