drm/xe/irq: Drop commented-out code for non-existent media engines

drm/xe/irq: Drop commented-out code for non-existent media engines

Although the hardware team has set aside some register bits for extra
media engines, no platform supported by the Xe driver today has VCS4-7
or VECS2-3.  Drop the corresponding code (which was already commented
out); we can bring it back easily enough if such engines show up on a
future platform.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20230401002106.588656-8-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>