remove taxonomy_other support

The initial release of this module supported taxonomy_other 6.x-1.1 since it seemed to be a simple and very desirable feature.
Nevertheless, that module seems to be planing taking care of a lot of feature requests which will deviate it from its original purpose, making it a lot more complex and therefore more unstable.

This module won't take the responsibility of keeping track of all those features carrying consequently error reporting casuistic (since it doesn't seem to have it by its own until now).

If someone thinks having similar functionality as taxonomy_other would be desirable for single free tagging vocabularies, please open a new issue on this module to re-check the status of taxonomy_other or start a new module to take care of "other" option for flat vocabularies.
Otherwise, you may file a new issue on taxonomy_other's issue queue to support this module.