compositor-drm: remove framebuffers while session is inactive

Avoid potentially unscrupulous new drm master from guessing and reading
framebuffers after a vt switch.
Track framebuffers and remove them during session deactivation,
re-adding them during session activation.

Signed-off-by: Robert Beckett <bob.beckett@collabora.com>
2 jobs for vt_fb_rm in 1 minute and 28 seconds (queued for 3 minutes and 3 seconds)
latest
Status Job ID Name Coverage
  Container Prep
passed #277122
container_prep

00:00:42

 
  Build
passed #277123
build-native-meson

00:00:45