All remote subcommands are spelled out words except 'rm'. 'rm', being a
popular UNIX command name, may mislead users that there are also 'ls' or
'mv'. Use 'remove' to fit with the rest of subcommands.

'rm' is still supported and used in the test suite. It's just not
widely advertised.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>