Trim memory.

        Args:
            level: HIDDEN | RUNNING_MODERATE | BACKGROUNDRUNNING_LOW | \
                     MODERATE | RUNNING_CRITICAL | COMPLETE

def app_trim_memory(self, pid: int or str, level: str = 'RUNNING_LOW') -> None:
        '''Trim memory.

        Args:
            level: HIDDEN | RUNNING_MODERATE | BACKGROUNDRUNNING_LOW | \
                     MODERATE | RUNNING_CRITICAL | COMPLETE
        '''
        _, error = self._execute('-s', self.device_sn, 'shell',
                                 'am', 'send-trim-memory', str(pid), level)
        if error and error.startswith('Error'):
            raise ApplicationsException(error.split(':', 1)[-1].strip())