present: Rename window_msc variable in present function

The value is not the current msc of the window, but the target value
the client sets independently of the window speicific msc offset. Make
this clearer.

Signed-off-by: Roman Gilg <subdiff@gmail.com>
3 jobs for cleanupTargetMscCalc in 6 minutes and 3 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Docker Image
passed #367763
debian-testing

00:00:27

 
  Build And Test
passed #367764
autotools-build-and-test

00:05:35

passed #367765
meson-build-and-test

00:01:53