src/utils_tail: Remove newline characters at the end of a line.

The tool is supposed to work line-based, so a) the newline character is
implicit and b) imho, does not belong to the string which is then further
processed.

Also, this allows '$' to match the end of a line when applying a regex to the
line, no matter if the REG_NEWLINE flag has been used when compiling the regex
or not.