drm/i915: remove CNL leftover

We left the definition IS_CANNONLAKE() macro while removing it from the
tree due to having to merge the changes in different branches. Now that
everything is back in sync and nobody is using IS_CANNONLAKE(), we can
safely ditch it.
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211021181847.1543341-1-lucas.demarchi@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -1455,7 +1455,6 @@ IS_SUBPLATFORM(const struct drm_i915_private *i915,
 #define IS_GEMINILAKE(dev_priv)	IS_PLATFORM(dev_priv, INTEL_GEMINILAKE)
 #define IS_COFFEELAKE(dev_priv)	IS_PLATFORM(dev_priv, INTEL_COFFEELAKE)
 #define IS_COMETLAKE(dev_priv)	IS_PLATFORM(dev_priv, INTEL_COMETLAKE)
-#define IS_CANNONLAKE(dev_priv)	0
 #define IS_ICELAKE(dev_priv)	IS_PLATFORM(dev_priv, INTEL_ICELAKE)
 #define IS_JSL_EHL(dev_priv)	(IS_PLATFORM(dev_priv, INTEL_JASPERLAKE) || \
 				IS_PLATFORM(dev_priv, INTEL_ELKHARTLAKE))