[native][web] Clean up dead conditions for media encryption

Summary:
In D13890 and D13891 some hardcoded switches were flipped, producing a dead code.
Removed unnecessary conditions and simplified code a bit.

Depends on D13891

Test Plan: Flow, eslint, test plans from D13890, D13891 to check for regressions

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13892