[serverctl] rename remove_cube to drop_cube (closes #4545093) For the sake of consistency, since commands are currently named: - add_{cube,entity,attribute,relation} - drop_{entity,attribute,relation} - remove_cube

usr/bin/cubicweb-ctl usr/bin/
usr/lib/PY_VERSION/*-packages/cubicweb/cwctl.py
../cubicweb-ctl.bash_completion etc/bash_completion.d/cubicweb-ctl