Simplify is_better_update condition

[dapplion]

If new_has_supermajority != old_has_supermajority

new	old	new > old
1	0	1
0	1	0

So the statement is equivalent to just new_has_supermajority

[hwwhww]

While it is more brief, I'm not sure if it is more readable as well.

[dapplion]

It's already used in the same function in

consensus-specs/specs/altair/light-client/sync-protocol.md

Lines 220 to 221 in fcd905c

	if new_has_relevant_sync_committee != old_has_relevant_sync_committee:
	return new_has_relevant_sync_committee

and

consensus-specs/specs/altair/light-client/sync-protocol.md

Lines 226 to 227 in fcd905c

	if new_has_finality != old_has_finality:
	return new_has_finality