Current Synapse still documents and registers
`/_matrix/client/.../account/deactivate` on client-serving workers when
auth is not delegated. MDAD already routes neighboring account endpoints
such as `account/3pid` and `account/whoami`, but it omitted
`account/deactivate` from both its client-reader bucket and its broader
generic-worker endpoint list.

Add the missing route patterns so MDAD's worker routing matches the
current upstream worker surface in non-delegated-auth deployments. In
MAS / MSC3861 mode the endpoint is not registered upstream anyway, so
this does not expand the effective delegated-auth surface.

Refs:
- b99a58719b/docs/workers.md (synapseappgeneric_worker)
- b99a58719b/synapse/rest/client/account.py (L284-L324)
- b99a58719b/synapse/rest/client/account.py (L913-L920)