Bluetooth: Demote ObsoleteSdkInt to a warning

ObsoleteSdkInt is failing when Bluetooth is built with
UNBUNDLED_BUILD_TARGET_SDK_WITH_API_FINGERPRINT=true.

To unblock the build, the error is demoted to a warning
with a TODO to add it back.

Bug: 318814235
Bug: 318719701
Change-Id: I2026a55fcc0b0d919107b620716e45d2154e4c77
Flag: Exempt, Build Change
Test: UNBUNDLED_BUILD_TARGET_SDK_WITH_API_FINGERPRINT=true m lint-check