DDLTask.handleRemoveMm() assumes locks not present

This moves every file in the table from under delta_x_x/ to root of the table/partition
How would this work for bucketed tables? Will it create bucket_x_copy_N files?
This could create 1000s of copy_N files - this will likely break something

The comments in the method assume locks are present - this would imply that there are appropriate Read/WriteEntity objects already created - I doubt this is the case for a table property change.

It seems like this kind of op should require an Exclusive lock at table level to prevent concurrent inserts (into new delta_x_x/)