Remove content description for BP Sfps Coex unlock icon

Unlock icon does not have any functionality for BP Sfps coex. Should
not have any content description.

Fixes: 293321861
Test: atest SystemUITests:com.android.systemui.biometrics
Flag: None
Change-Id: I4bf2b3a221e0ed2f7932534d2232b38920d3df42