[mms] Fix migrations nos. 4 & 5.
Released Horde_History-2.1.3
Development mode for Horde_History-2.1.4
[mms] Fix usage of removeIndex().

Sigh.  Documentation is unclear that you can't do this (not to mention
this behavior is the opposite of what addIndex does).
Released Horde_History-2.1.4
Development mode for Horde_History-2.1.5