Undo attempts to cache private keys aggressively
Undo attempts to cache private keys aggressively

This was triggering security prompts at random times (after any device list
update).

Fixes https://github.com/vector-im/element-web/issues/15250

matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk