Fix recovery OTA error on merged targets

Currently, when merging target files, system side's update_engine
version info is copied into the merged target_files. This causes
recovery OTA failure, because update_engine_sideload daemon in recovery
is from vendor side. To fix it, use the older version of update_engine
config when merging target files.

Test: th
Bug: 257426678
Change-Id: I5d3304366749995c99a61ca0645a22ee047f1465