Revert "meson: dv plugin now works on MSVC"

This reverts commit 05a89613.

Let's not put in stuff that needs unreleased Meson. This can go in
for the next cycle.

ext/meson.build

@@ -5,7 +5,10 @@ subdir('gdk_pixbuf')
 subdir('jack')
 subdir('jpeg')
 # subdir('libcaca')
-subdir('dv')
+# FIXME: dv plugin fails to link with msvc, wants pthread.lib
+if cc.get_id() != 'msvc'
+  subdir('dv')
+endif
 subdir('libpng')
 # subdir('raw1394')
 subdir('pulse')