Remove flag btsec_le_oob_pairing

Test: m libbluetooth
Bug: 374376990
Bug: 315241296
Flag: com.android.bluetooth.flags.btsec_le_oob_pairing
Ignore-AOSP-First: security
Tag: #security
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:0f5a7b3433c93e587bc5491b1647c208cfc04c38)
Merged-In: I3e4b0ca2f191b0bd1e27bd933b84ed4e900ba971
Change-Id: I3e4b0ca2f191b0bd1e27bd933b84ed4e900ba971