Use tor_api.h entry points in ntmain.c.

When we updated main.c to use the same entry points as tor_api.h, we
didn't update ntmain.c.  This led to bugs as the two got out of
sync.

There are two calls that we drop in this patch: first, I drop the
call to set_main_thread(), since that's redundant with the init
function in compat_winthreads.c (but see #32884).  Second, I drop
the check for CMD_RUN_TOR: I'll add that back with a subsequent
commit.

Closes ticket 32883.

changes/bug32883

@@ -0,0 +1,5 @@
+  o Code simplification and refactoring (windows services):
+    - The windows service logic now uses the tor_api.h entry points, to
+      avoid needless code duplication, and to prevent bugs related to
+      the different entry points getting out of sync.  Closes ticket
+      32883.