drm/i915: Remove unused enable_cmd_parser modparam

drm/i915: Remove unused enable_cmd_parser modparam

The command parser is feature complete, stable and required by
userspace. In commit 41736a8e3331 ("drm/i915: Use the precomputed value
for whether to enable command parsing") I accidentally removed control
from the modparam, and as no one has complained, remove the left
over modparam completely!

References: 41736a8e3331 ("drm/i915: Use the precomputed value for whether to enable command parsing")
Signed-off-by: Chris Wilson <[email protected]>
Cc: Joonas Lahtinen <[email protected]>
Cc: Jani Nikula <[email protected]>
Acked-by: Jani Nikula <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]