Remove bogus "perl not found" on Windows.

Testing exit code from popen(), comparing it with 1, and deciding that
perl.exe is not there, is a) wrong conclusion, and b) uninteresting,
because MTR always runs with perl, and with MTR_PERL set.

Background:
Recent change in 7af50e4d introduced
exit code 1 from perl snippet, that broke Windows CI. Do not want
to debug this ever again.

client/mysqltest.cc

@@ -4648,15 +4648,11 @@ void do_perl(struct st_command *command)
 
     /* Check for error code that indicates perl could not be started */
     int exstat= WEXITSTATUS(error);
-#ifdef _WIN32
-    if (exstat == 1)
-      /* Text must begin 'perl not found' as mtr looks for it */
-      abort_not_supported_test("perl not found in path or did not start");
-#else
+#ifndef _WIN32
     if (exstat == 127)
       abort_not_supported_test("perl not found in path");
-#endif
     else
+#endif
       handle_command_error(command, exstat, my_errno);
   }
   dynstr_free(&ds_delimiter);