Remove SystemApi annotation from EuiccManager.getOtaStatus()

EuiccManager.getOtaStatus() has been annotated as @SystemApi, but its
declaring class EuiccManager has not. Therefore, the method hasn't been
recognized as SystemApi (does not appear in system-current.txt) and no
app is using the method.

This hasn't been harmful, but will soon trigger CTS failures when we do
the exact match for SystemAPIs; a runtime entity annotated as @SystemApi
have to exist in the documented API (e.g. system-current.txt). So
removing this no-op annotation.

Bug: 67891551
Test: m -j checkapi
Change-Id: I570ef5e5c88b6b9162116d3d3a7b17367efa9d7f