Remove create_bwc_indexes.py (elastic/x-pack-elasticsearch#2989)
Remove create_bwc_indexes.py (elastic/x-pack-elasticsearch#2989)

This commit removes the create_bwc_indexes.py script as we no longer need this script to test for
BWC with indices. The last test relying on this script was removed in elastic/x-pack-elasticsearch#2832.

relates elastic/x-pack-elasticsearch#1629

Original commit: elastic/x-pack-elasticsearch@f7321c99db614c2ef909bed4907d21cd852d9e78

strapdata/elassandra,strapdata/elassandra,strapdata/elassandra,vroyer/elassandra,vroyer/elassandra,strapdata/elassandra,strapdata/elassandra,vroyer/elassandra