{Role} az role assignment create: Refine help message for --name (#24926)

Author: jiasli

src/azure-cli/azure/cli/command_modules/role/_params.py

@@ -301,7 +301,6 @@ def load_arguments(self, _):
         c.argument('resource_group_name', options_list=['--resource-group', '-g'], help='use it only if the role or assignment was added at the level of a resource group')
 
     with self.argument_context('role assignment') as c:
-        c.argument('role_assignment_name', options_list=['--name', '-n'])
         c.argument('role', help='role name or id', completer=get_role_definition_name_completion_list)
         c.argument('show_all', options_list=['--all'], action='store_true', help='show all assignments under the current subscription')
         c.argument('include_inherited', action='store_true', help='include assignments applied on parent scopes')
@@ -317,7 +316,7 @@ def load_arguments(self, _):
         c.argument('condition', is_preview=True, min_api='2020-04-01-preview', help='Condition under which the user can be granted permission.')
         c.argument('condition_version', is_preview=True, min_api='2020-04-01-preview', help='Version of the condition syntax. If --condition is specified without --condition-version, default to 2.0.')
         c.argument('assignment_name', name_arg_type,
-                   help='Name of the role assignment. If omitted, a new GUID is generetd.')
+                   help='A GUID for the role assignment. It must be unique and different for each role assignment. If omitted, a new GUID is generetd.')
 
     time_help = ('The {} of the query in the format of %Y-%m-%dT%H:%M:%SZ, e.g. 2000-12-31T12:59:59Z. Defaults to {}')
     with self.argument_context('role assignment list-changelogs') as c: