Remove dead neonDrawLighting code

FELightingNEON.h's inline FELighting::platformApplyNeon() method refers
to an extern neonDrawLighting symbol.  This function is implemented in
assembly in WebKit but does not exist in blink.  This must then be dead
code (otherwise there would have been complaints).

The only reference to platformApplyNeon that I can find is an ifdef'ed
call in FELighting::platformApply(), which is only enabled if the target
supports NEON but not Thumb (which I guess must be very uncommon).

BUG=381082
TEST=build with arm_neon=1 arm_thumb=0

Review URL: https://codereview.chromium.org/313303003

git-svn-id: svn://svn.chromium.org/blink/trunk@176365 bbb929c8-8fbe-4397-9dbb-9b2b20218538