Move some utility methods from portal to separate files

mautrix_telegram/util/__init__.py

@@ -1,7 +1,4 @@
 from .color_log import ColorFormatter
-from .deduplication import PortalDedup
 from .file_transfer import convert_image, transfer_file_to_matrix
-from .media_fallback import make_contact_event_content, make_dice_event_content
 from .parallel_file_transfer import parallel_transfer_to_telegram
 from .recursive_dict import recursive_del, recursive_get, recursive_set
-from .send_lock import PortalSendLock