redhat_subscription: drop unneeded args to Rhsm.register() (#5583)

Stop passing all the "rhsm_", and "server_" module arguments to
"Rhsm.register()", and thus as arguments for
"subscription-manager register":
- right before calling "Rhsm.register()", "Rhsm.configure()" is called
  to configure subscription-manager with all the "rhsm_", and "server_"
  arguments; hence, they are already configured
- the passed argument to "--serverurl" is partially wrong:
  "Rhsm.register()" passes only the hostname, whereas the other bits
  (port and prefix) are supported too; this "works" because port and
  prefix were already configured previously, and the lax parsing that
  subscription-manager does allows for missing bits
- the parsing done by subscription-manager for "--baseurl" strips out
  the URL scheme and always uses https: this means that specifying
  "rhsm_baseurl: http://server" as module parameter will be taken as
  "https://server" by subscription-manager; since "rhsm_baseurl" is
  already configured by "Rhsm.configure()", this issue is gone

tests/unit/plugins/modules/test_redhat_subscription.py

@@ -92,7 +92,6 @@ TEST_CASES = [
                 ),
                 (
                     ['/testbin/subscription-manager', 'register',
-                        '--serverurl', 'satellite.company.com',
                         '--username', 'admin',
                         '--password', 'admin'],
                     {'check_rc': True, 'expand_user_and_vars': False},
@@ -180,7 +179,6 @@ TEST_CASES = [
                     [
                         '/testbin/subscription-manager',
                         'register',
-                        '--serverurl', 'satellite.company.com',
                         '--org', 'admin',
                         '--activationkey', 'some-activation-key'
                     ],
@@ -340,9 +338,6 @@ TEST_CASES = [
                         'register',
                         '--force',
                         '--org', 'admin',
-                        '--proxy', 'proxy.company.com:12345',
-                        '--proxyuser', 'proxy_user',
-                        '--proxypassword', 'secret_proxy_password',
                         '--username', 'admin',
                         '--password', 'admin'
                     ],