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/nsupdate/tests.sh

@@ -357,7 +357,7 @@ digcomp dig.out.ns1 dig.out.ns2 || ret=1
 
 echo_i "SIGKILL and restart server ns1"
 cd ns1
-$KILL -KILL `cat named.pid`
+kill -KILL `cat named.pid`
 rm named.pid
 cd ..
 sleep 10
@@ -400,13 +400,8 @@ END
 
 sleep 5
 
-if [ ! "$CYGWIN" ]; then
-    echo_i "SIGHUP secondary"
-    $KILL -HUP `cat ns2/named.pid`
-else
-    echo_i "reload secondary"
-    rndc_reload ns2 10.53.0.2
-fi
+echo_i "SIGHUP secondary"
+kill -HUP `cat ns2/named.pid`
 
 sleep 5
 
@@ -424,13 +419,8 @@ END
 
 sleep 5
 
-if [ ! "$CYGWIN" ]; then
-    echo_i "SIGHUP secondary again"
-    $KILL -HUP `cat ns2/named.pid`
-else
-    echo_i "reload secondary again"
-    rndc_reload ns2 10.53.0.2
-fi
+echo_i "SIGHUP secondary again"
+kill -HUP `cat ns2/named.pid`
 
 sleep 5