Remove calendar-proxy support - did this ever work?

apps/dav/lib/connector/sabre/principal.php

@@ -147,8 +147,6 @@ class Principal implements BackendInterface {
 				return $this->principalPrefix . '/' . $group->getGID();
 			}, $groups);
 
-//			$groups[]= $this->principalPrefix . '/' . $name . '/calendar-proxy-read';
-//			$groups[]= $this->principalPrefix . '/' . $name . '/calendar-proxy-write';
 			return $groups;
 		}
 		return [];

apps/dav/tests/unit/connector/sabre/principal.php

@@ -211,10 +211,7 @@ class Principal extends TestCase {
 			->method('getUserGroups')
 			->willReturn([]);
 
-		$expectedResponse = [
-			'principals/users/foo/calendar-proxy-read',
-			'principals/users/foo/calendar-proxy-write'
-		];
+		$expectedResponse = [];
 		$response = $this->connector->getGroupMembership('principals/users/foo');
 		$this->assertSame($expectedResponse, $response);
 	}