Make exit flag depend on ports 80 and 443, not 6667
In the discussion around #22820 (moved), we decided that giving the exit flag to relays that exit to ports 80 and 443 is the right thing to do:
First, port 6667 used to be relevant, but now, and especially with the advent of ircs, it isn't.
Second, we invented the current algorithm for the Exit flag back before Mike invented the 'reduced exit policy'.
Third, a relay that exits to 443 but not 80, or 80 but not 443, is going to make web browsing super bumpy when used with Tor Browser's tab isolation strategy.
So we should simplify it.