drop AbortSignal.timeout

[keithamus]

AbortSignal timeout was added to Safari 16. Now Safari 18 is out, it might be a good time to consider dropping this polyfill as we close in on 0.5% total unsupported. No individual browser is more than 0.3% and we can see support in the more experimental browsers; Ladybird has implemented this feature (although Servo has yet to).

timeout() static method

Browser	Supported Since	Latest Version	% Supported	% Unsupported
chrome	103	128	68.424	0.289
edge	103	128	11.049	0.037
firefox	100	130	12.108	0.021
firefox_android	100	130	0.362	0.000
ie	Not Supported		0.000	0.002
opera	89	111	1.437	0.048
safari	16	17.6	3.848	0.070
safari_ios	16	17.6	1.342	0.061
webview_android	103	128	0.007	0.024
Total:			98.577	0.552

(Note: "Other" browsers make up 0.871%)