DRM: delete DRM IRQ legacy midlayer docs

Remove documentation associated with the removal of the DRM IRQ legacy
midlayer.

Eliminates these documentation warnings:

../drivers/gpu/drm/drm_irq.c:1: warning: 'irq helpers' not found
../drivers/gpu/drm/drm_irq.c:1: warning: no structured comments found

Fixes: c1736b9 ("drm: IRQ midlayer is now legacy")
Signed-off-by: Randy Dunlap <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Cc: Sam Ravnborg <[email protected]>
Cc: [email protected]
Cc: Jonathan Corbet <[email protected]>
Cc: [email protected]
Cc: David Airlie <[email protected]>
Cc: Daniel Vetter <[email protected]>
Signed-off-by: Thomas Zimmermann <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Signed-off-by: Maarten Lankhorst <[email protected]>

Author: rddunlap

Documentation/gpu/drm-internals.rst

@@ -111,15 +111,6 @@ Component Helper Usage
 .. kernel-doc:: drivers/gpu/drm/drm_drv.c
    :doc: component helper usage recommendations
 
-IRQ Helper Library
-~~~~~~~~~~~~~~~~~~
-
-.. kernel-doc:: drivers/gpu/drm/drm_irq.c
-   :doc: irq helpers
-
-.. kernel-doc:: drivers/gpu/drm/drm_irq.c
-   :export:
-
 Memory Manager Initialization
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~