Revert "drm/i915: Force clean compilation with -Werror"

This reverts commit 118182e9d7.

It's causing too much trouble when compile-testing for non-i915 folks.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

drivers/gpu/drm/i915/Kconfig.debug

@@ -1,5 +0,0 @@
-config DRM_I915_WERROR
-	bool "Force GCC to throw an error instead of a warning when compiling"
-	default n
-	---help---
-	  Add -Werror to the build flags for (and only for) i915.ko