Clean up Perl code according to perlcritic

Fix all perlcritic warnings of severity level 5, except in
src/backend/utils/Gen_dummy_probes.pl, which is automatically generated.

Reviewed-by: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>

src/interfaces/ecpg/preproc/check_rules.pl

@@ -53,8 +53,8 @@ my $comment     = 0;
 my $non_term_id = '';
 my $cc          = 0;
 
-open GRAM, $parser or die $!;
-while (<GRAM>)
+open my $parser_fh, '<', $parser or die $!;
+while (<$parser_fh>)
 {
 	if (/^%%/)
 	{
@@ -145,7 +145,7 @@ while (<GRAM>)
 	}
 }
 
-close GRAM;
+close $parser_fh;
 if ($verbose)
 {
 	print "$cc rules loaded\n";
@@ -154,8 +154,8 @@ if ($verbose)
 my $ret = 0;
 $cc = 0;
 
-open ECPG, $filename or die $!;
-while (<ECPG>)
+open my $ecpg_fh, '<', $filename or die $!;
+while (<$ecpg_fh>)
 {
 	if (!/^ECPG:/)
 	{
@@ -170,7 +170,7 @@ while (<ECPG>)
 		$ret = 1;
 	}
 }
-close ECPG;
+close $ecpg_fh;
 
 if ($verbose)
 {