[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
addressbook
basket
blog
book
calendar
comment
company
email
file
folder
i18ncontent
keyword
link
mailinglist
person
tag
timeseries
vcsfile