Remove catch handlers in private key retrieval
Remove catch handlers in private key retrieval

This removes some catch blocks originally added by
https://github.com/matrix-org/matrix-js-sdk/pull/1472 so that higher level
operations can handle them as needed.

Part of https://github.com/vector-im/element-web/issues/15584

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