i2ptunnel: Remove nonstandard Proxy-Connection header (Gitlab #452)

from all error pages, and strip in the client and server proxies Note: conflicts with MR !129 (closed) in a couple spots

Closes #452 (closed)

changed milestone to %2.5.0

added i2ptunnel minor labels

assigned to @zzz

approved this merge request

Thank you for the review and approval. I hadn't planned to merge this for 2.4.0. I2PPlus just merged it so I'd like to at least wait a week or so to hear of test results from them.

If 2.4.0 slips again maybe I'd go ahead and merge it but there's no rush.

changed milestone to %2.4.0

merged

mentioned in commit 34bff080