The replace_entry() function is nothing more than a convenience for
calling delete_old_entry() and then create_entry(). But it is only used
once in the code, and we can just open-code the two calls instead of
the one.
The reason I want to change it now is that the shortcut replace_entry()
helped hide a bug (#11801) - replace_entry() works incorrectly if the
old and new row have the same key, because if they do we get a deletion
and creation of the same row with the same timestamp - and the deletion
wins. Having the two calls not hidden by a convenience function makes
this potential problem more apparent.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>