Revert "Add read_channel_content permission (#24018)" (#24114)

This reverts commit a19ce047ba.

server/channels/store/sqlstore/integrity_test.go

@@ -258,7 +258,6 @@ func createDefaultRoles(ss store.Store) {
 		DisplayName: model.ChannelUserRoleId,
 		Permissions: []string{
 			model.PermissionReadChannel.Id,
-			model.PermissionReadChannelContent.Id,
 			model.PermissionCreatePost.Id,
 		},
 	})
@@ -268,7 +267,6 @@ func createDefaultRoles(ss store.Store) {
 		DisplayName: model.ChannelGuestRoleId,
 		Permissions: []string{
 			model.PermissionReadChannel.Id,
-			model.PermissionReadChannelContent.Id,
 			model.PermissionCreatePost.Id,
 		},
 	})