Bug 1387185 - remove --enable-png-arm-neon-support from moz.configure whitelist; r=mshal

This option does not exist in the old configure.

build/moz.configure/old.configure

@@ -202,7 +202,6 @@ def old_configure_options(*options):
     '--enable-optimize',
     '--enable-parental-controls',
     '--enable-pie',
-    '--enable-png-arm-neon-support',
     '--enable-posix-nspr-emulation',
     '--enable-pref-extensions',
     '--enable-pulseaudio',