Improve changelog script

The changelog message taken from the tags in the turris-build repository are signed often and so the message ends on:

-----END PGP SIGNATURE-----

However, if the tag is not signed, the last line is the last line of the changelog so this pop() will remove the important data.

I don't see why to pop the last element at all, as the format of the line will not pass the regex.

On top of it, remove console log messages which are not needed in production.