Remove leftover test code for Windows

- Removed all code that only runs under CYGWIN, and made all
  code that doesn't run under CYGWIN non-optional.
- Removed the $TP variable which was used to add optional
  trailing dots to filenames; they're no longer optional.
- Removed references to pssuspend and dos2unix.
- No need to use environment variables for diff and kill.
- Removed uses of "tr -d '\r'"; this was a workaround for
  a cygwin regex bug that is no longer needed.

bin/tests/system/checkzone/tests.sh

@@ -192,7 +192,7 @@ status=`expr $status + $ret`
 
 ret=0
 # Step 3: Ensure that output conversion from stdin is the same as the output conversion from a file.
-$DIFF zones/zone1_file.txt zones/zone1_stdin.txt >/dev/null 2>&1 || ret=1
+diff zones/zone1_file.txt zones/zone1_stdin.txt >/dev/null 2>&1 || ret=1
 status=`expr $status + $ret`
 
 if [ $ret != 0 ]; then echo_i "failed"; fi