Remove command checks in tests of pg_basebackup and pg_receivewal
The TAP tests of those commands have been checking if commands of "gzip"
and "lz4" existed by launching them with an extra --version. Based on
the buildfarm, this is not required for "gzip" as the command always
exists. Since
1d084fb, "lz4" has a ./configure check doing the same
thing.
Reported-by: Andres Freund
Discussion: https://postgr.es/m/
20220212220643.ozuvq2k4cjkcnr2v@alap3.anarazel.de
Discussion: https://postgr.es/m/Ygm2ADakjlqGc2Ro@paquier.xyz