Fix faulty decoded-time adjustment in erc-stamp

* lisp/erc/erc-stamp.el (erc-stamp--lr-date-on-pre-modify): Remove
disruptive assertion for now.
(erc-stamp--time-as-day): Attempt to fix date being rewound by a whole
day when daylight saving time is in effect.  Do this by forcing the
`dst' slot of the `decoded-time' object to -1 and the `zone' to nil.
1 job for master in 3 minutes and 48 seconds (queued for 1 minute and 51 seconds)
Status Job ID Name Coverage
  Normal
failed #82335
test-lisp-erc-inotify

00:03:48

 
Name Stage Failure
failed
test-lisp-erc-inotify Normal
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Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1