As of GNU Emacs 30.1 it's not possible to delete the first line of the
calc trail visible after invoking the Emacs calculator.

To reproduce:

1. Start Emacs calc: C-x * c
2. Enter a few numbers: 10 RET 20 RET 30 RET
3. Try deleting the trail lines, repeat for each line: t k

Expected behavior: all the trail lines are being deleted.

Actual behavior: the first line is still left, no error is reported.

This bug was introduced in commit
8e1376a39125c3ffc0484077b502444d853eca79, included since Emacs 28.1.
Before that commit, calc trail used its first line as a header, which
wasn't meant to be deleted.  After migrating to using header-line, the
code preserving the first line was kept intact, still preventing the
removal of the first line even though it's no longer special.

I'm attaching a patch fixing this behavior.

Best regards
-- 
Wojciech Siewierski