doc/rgw: fix radosgw-admin command names in man page

doc/rgw: fix radosgw-admin command names in man page

The man page documented several commands with incorrect names that do not match the actual implementation in radosgw-admin.cc:

- period rm -> period delete

- zone rm -> zone delete

- role rm -> role delete

- role-policy rm -> role-policy delete

Cross-referenced all rm/delete commands with the source code to ensure documentation matches actual command names.

Signed-off-by: Farzan <farzan.eng@gmail.com>