std: remove misleading doc of UdpSocket::send_to/send

[xizheyin]

Fixes #145862

I think the most misleading expression is that UDP transmits data as packets rather than as streams, so it appears that partial writes does not occur?

Additionally, the code might consider checking to see if buffer length exceeds the 16-byte limit, and erroring early as a small optimization, during the clamping of buffer length.

For this suggestion in #145862, I think the check should be managed by OS. Either the packet is accepted, or the operating system generates an error, such as EMSGSIZE.

r? libs

[ibraheemdev]

This is pretty minor but it adds the guarantee that partial writes never occur. r? libs-api

[Amanieu]

This was added in #105394. See #105394 (comment)

cc @workingjubilee @Patiga