fix: revert incorrect servername fix

[szmarczak]

This reverts commit 2ee6e37 which incorrectly allowed IP server names.

Sorry for my mistake. Got confused by https://github.com/nodejs/node/blob/e5670f49682ced87451e5fc1e56d7d3fc396c6f2/lib/internal/http2/core.js#L623-L639 incorrectly returning https://false:443 for IP addresses. However, I did not investigate further. Per RFC6066:

Currently, the only server names supported are DNS hostnames;
[...]
"HostName" contains the fully qualified DNS hostname of the server
[...]
Literal IPv4 and IPv6 addresses are not permitted in "HostName".

Again I'm deeply sorry for my mistake.

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Node.js also gives a warning when the servername is an IP address. I must've missed it somehow :(

[codecov-commenter]

Codecov Report

Merging #1005 (2da32c0) into main (c57aac5) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1005   +/-   ##
=======================================
  Coverage   94.03%   94.03%           
=======================================
  Files          37       37           
  Lines        3585     3589    +4     
=======================================
+ Hits         3371     3375    +4     
  Misses        214      214           

Impacted Files	Coverage Δ
lib/core/util.js	99.10% <100.00%> (+0.03%)	⬆️

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[mcollina]

lgtm