OpenSSL::Test::__fixup_prg: don't check program existence

The program will fail to run if it doesn't exist anyway, no need to
check its existence here.

Fixes #4306
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4309)

util/perl/OpenSSL/Test.pm

@@ -1084,11 +1084,6 @@ sub __fixup_prg {
 	$prefix = ($prog =~ /^(?:[\$a-z0-9_]+:)?[<\[]/i ? "mcr " : "mcr []");
     }
 
-    # We test if the program to use exists.
-    if ( ! -x $prog ) {
-	$prog = undef;
-    }
-
     if (defined($prog)) {
 	# Make sure to quotify the program file on platforms that may
 	# have spaces or similar in their path name.