pgsql: Remove command checks in tests of pg_basebackup and pg_receivewa

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

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a4e1deb42b378650aaa2bcb3897caad9fe895957

Modified Files
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src/bin/pg_basebackup/t/010_pg_basebackup.pl |  5 ++---
src/bin/pg_basebackup/t/020_pg_receivewal.pl | 10 ++++------
2 files changed, 6 insertions(+), 9 deletions(-)