drm/msm/a6xx: Remove duplicate irq disable from remove

a6xx_gmu_stop() already calls this function via shutdown or force_stop,
so it's not necessary to call it twice. Previously this would have
knocked the irq refcount out of sync, but now with the irqs_enabled flag
it's just housekeeping.

Changes in v2:
- None

Cc: Jordan Crouse <jcrouse@codeaurora.org>
Reviewed-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190523171653.138678-2-sean@poorly.run