It seems to work for me if I use warnings; use strict;, then change != to ne:

use strict;
use warnings;
use Data::Dumper;

my $co = 'b';
my @allcompanies = qw(a b c d);
print Dumper(\@allcompanies);
@allcompanies = grep { $_ ne $co } @allcompanies;
print Dumper(\@allcompanies);

__END__

$VAR1 = [
          'a',
          'b',
          'c',
          'd'
        ];
$VAR1 = [
          'a',
          'c',
          'd'
        ];
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