Merge branch 'PR/dmesg-delta-notime' of https://github.com/karelzak/util-linux-work

* 'PR/dmesg-delta-notime' of https://github.com/karelzak/util-linux-work:
  dmesg: rename is_time_fmt_set() to is_time_fmt()
  dmesg: warn on boot time failure instead of suppressing timestamps
  dmesg: add replace_time_fmt() and replace_delta_fmt() helpers
  tests: add dmesg -d -t and -t -d timestamp format tests
  dmesg: fix -d -t (--show-delta --notime) output regression
  dmesg: remove delta variable, use time format list consistently