Remove remains of dead code around service discovery

search_timer is never used, just created and deleted.
wait_disc was used with search_timer, also no longer needed.
sdp_results is just set, never used.

bta_dm_disc_acl_down was used with search_timer to trigger next device
discovery - also not used anymore. SDP would return proper error code
when disconnection happens during SDP.

Bug: 330675788
Bug: 335732980
Flag: com.android.bluetooth.flags.separate_service_and_device_discovery
Test: mma -j32
Change-Id: Ibd53edcebcd414b9f2e4252aa9b6eff81d0ec3eb