Remove all references of `m.room.aliases` in react and js-sdk

[bwindels]

All tasks mentioned in #12337 have been implemented as part of MSC2432, but when searching for m.room.aliases in the code, there are still a few occurrences. I've postponed getting rid of those because we're still in the cross-signing sprint, but afterwards we probably want to clean that up.

m.room.aliases references to remove

matrix-react-sdk:

• src/SlashCommands.tsx#L728
• src/Unread.ts#L45
• test/Unread-test.ts#L106

matrix-js-sdk:

• src/@types/event.ts#L36-L39
• src/models/room.ts#L1378
• src/models/event.ts#L1588
• src/models/room.ts#L1383

[MadLittleMods]

Added a list of references to clean-up to the description.

Looks like a pretty easy technical debt to resolve.