Revert output string parsing to detect broken replication

[rustprooflabs]

Details

The approach I took in #392 to fix #391 was a result of getting an invalid returncode=0 when there was an error.

Hoping that osm2pgsql-dev/osm2pgsql#2206 can lead to getting the returncode set properly. If it does, the line parsing for specific error text can be removed.

[rustprooflabs]

This one will be ready to work on after osmcode/pyosmium#257 is closed.