Stop using PQsendQuery in libpq_pipeline
The "emulation" I wrote for PQsendQuery in pipeline mode to use extended
query protocol, in commit
acb7e4eb6b1c, is problematic. Due to numerous
bugs we'll soon remove it. As a first step and for all branches back to
14, stop using PQsendQuery in libpq_pipeline. Also remove a few test
lines that will no longer be relevant.
Backpatch to 14.
Discussion: https://postgr.es/m/CA+mi_8ZGSQNmW6-mk_iSR4JZB_LJ4ww3suOF+1vGNs3MrLsv4g@mail.gmail.com