Cleanup the last Windows / MSC ifdefs and comments

Cleanup the remnants of MS Compiler bits from <isc/refcount.h>, printing
the information in named/main.c, and cleanup some comments about Windows
that no longer apply.

The bits in picohttpparser.{h,c} were left out, because it's not our
code.

bin/tests/system/runtime/tests.sh

@@ -245,7 +245,7 @@ if [ "$(id -u)" -eq 0 ]; then
     if [ $ret -ne 0 ]; then echo_i "failed"; fi
     status=$((status+ret))
 else
-    echo_i "skipped, not running as root or running on Windows"
+    echo_i "skipped, not running as root"
 fi
 
 echo_i "exit status: $status"

bin/tests/system/shutdown/tests_shutdown.py

@@ -40,7 +40,7 @@ def do_work(named_proc, resolver, rndc_cmd, kill_method, n_workers, n_queries):
     if kill_method=="rndc" named will be asked to shutdown by
     means of rndc stop.
     if kill_method=="sigterm" named will be killed by SIGTERM on
-    POSIX systems or by TerminateProcess() on Windows systems.
+    POSIX systems.
 
     :param named_proc: named process instance
     :type named_proc: subprocess.Popen