Disable btif_gatt_check_encrypted_link.

It seems to cause redundant Security Requests that lead to pairing
prompts and bond loss on iOS paired watches. Removing this code
fixes the issue by partially bringing back the behavior used when
BLE_DELAY_REQUEST_ENC flag was enabled.

Test: manual - verified salmon paired with iOS 14.2 does not lose bond
Test:        - or trigger pairing alerts anymore.
Bug: 175785899
Bug: 263323082
Tag: #stability
Change-Id: I5fb3eca8419e79c72d067f3f38e1f952de266646
(cherry picked from commit 7c2fe92921e9b3d81d417bd33c079740270cbbe2)