Handle migration from meek-azure to meek built-in bridge type

We are renaming meek-azure to meek as the built-in bridges no longer use Microsoft Azure cloud hosting, so the name is vestigial.

We need to handle migrating old users who have selected meek-azure as their torbrowser.settings.bridges.builtin_type to just meek.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information