Remove unused # type: ignores (#12531)

Over time we've begun to use newer versions of mypy, typeshed, stub
packages---and of course we've improved our own annotations. This makes
some type ignore comments no longer necessary. I have removed them.

There was one exception: a module that imports `select.epoll`. The
ignore is redundant on Linux, but I've kept it ignored for those of us
who work on the source tree using not-Linux. (#11771)

I'm more interested in the config line which enforces this. I want
unused ignores to be reported, because I think it's useful feedback when
annotating to know when you've fixed a problem you had to previously
ignore.

* Installing extras before typechecking

Lacking an easy way to install all extras generically, let's bite the bullet and
make install the hand-maintained `all` extra before typechecking.

Now that https://github.com/matrix-org/backend-meta/pull/6 is merged to
the release/v1 branch.

synapse/storage/prepare_database.py

@@ -501,11 +501,11 @@ def _upgrade_existing_database(
 
                 if hasattr(module, "run_create"):
                     logger.info("Running %s:run_create", relative_path)
-                    module.run_create(cur, database_engine)  # type: ignore
+                    module.run_create(cur, database_engine)
 
                 if not is_empty and hasattr(module, "run_upgrade"):
                     logger.info("Running %s:run_upgrade", relative_path)
-                    module.run_upgrade(cur, database_engine, config=config)  # type: ignore
+                    module.run_upgrade(cur, database_engine, config=config)
             elif ext == ".pyc" or file_name == "__pycache__":
                 # Sometimes .pyc files turn up anyway even though we've
                 # disabled their generation; e.g. from distribution package