Do not call bta_dm_free_sdp_db when GATT discovery is complete

This call was recently added as part of
bta_dm_disc_stuck_in_cancelling_fix. If it's gatt discovery being
finished, call to bta_dm_free_sdp_db can cause crash, because p_sdp_db
would be null.

Also, as I gained better understanding this code, p_sdp_db should be
left to SDP related functions, not mixed with LE GATT discovery.

Bug: 330675788
Bug: 335732980
Flag: com.android.bluetooth.flags.separate_service_and_device_discovery
Test: mma -j32
Change-Id: If6bace692d968eb4121e896b5d813397d936e30b