memmove() should be used instead of memcpy() for overlapping memory regions.
Overlapping memory regions itself here are fine, because code simply removes
one element from arbitrary position of an array.
Just rename index in data dictionary and in InnoDB cache when it's possible.
Introduce ALTER_INDEX_RENAME for that purpose so that engines can optimize
such operation.
Unused code between macro MYSQL_RENAME_INDEX was removed.
compare_keys_but_name(): compare index definitions except for index names
Alter_inplace_info::rename_keys:
ha_innobase_inplace_ctx::rename_keys: vector of rename indexes
fill_alter_inplace_info():: fills Alter_inplace_info::rename_keys
