Bug 1822827 - Remove explicit NEON flags from skia build

Bug 1822827 - Remove explicit NEON flags from skia build

While Firefox builds for Android ARMv7 don't support non-NEON
processors, downstreams (including non-Android ones) may still want to
support them.

Because those Firefox builds don't support non-NEON processors, the NEON
flags are actually already passed globally, and they don't need to be
explicitly added. NEON_FLAGS is actually only meant to be used for
sources that specifically need NEON support even when the target doesn't
support it, for, e.g. specialized code behind runtime CPU detection.

Gbp-Pq: Topic porting
Gbp-Pq: Name Bug-1822827-Remove-explicit-NEON-flags-from-skia-bui.patch