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

src/bin/pg_basebackup/t/010_pg_basebackup.pl

@@ -768,8 +768,7 @@ SKIP:
 	my $gzip = $ENV{GZIP_PROGRAM};
 	skip "program gzip is not found in your system", 1
 	  if (!defined $gzip
-		|| $gzip eq ''
-		|| system_log($gzip, '--version') != 0);
+		|| $gzip eq '');
 
 	my $gzip_is_valid =
 	  system_log($gzip, '--test', @zlib_files, @zlib_files2, @zlib_files3);

src/bin/pg_basebackup/t/020_pg_receivewal.pl

@@ -130,8 +130,7 @@ SKIP:
 	my $gzip = $ENV{GZIP_PROGRAM};
 	skip "program gzip is not found in your system", 1
 	  if (!defined $gzip
-		|| $gzip eq ''
-		|| system_log($gzip, '--version') != 0);
+		|| $gzip eq '');
 
 	my $gzip_is_valid = system_log($gzip, '--test', @zlib_wals);
 	is($gzip_is_valid, 0,
@@ -186,8 +185,7 @@ SKIP:
 	my $lz4 = $ENV{LZ4};
 	skip "program lz4 is not found in your system", 1
 	  if (!defined $lz4
-		|| $lz4 eq ''
-		|| system_log($lz4, '--version') != 0);
+		|| $lz4 eq '');
 
 	my $lz4_is_valid = system_log($lz4, '-t', @lz4_wals);
 	is($lz4_is_valid, 0,