gitlog-to-changelog: Drop scripts in favour of gnulib version

The ChangeLog automation scripts were incorporated in gnulib as
vcs-to-changelog for a while now since other projects expressed the
desire to use and extend this script.  In the interest of avoiding
duplication of code, drop the glibc version of gitlog-to-changelog and
use the gnulib one directly.

The only file that remains is vcstocl_quirks.py, which specifies
properties and quirks of the glibc project source code.  This patch
also drops the shebang at the start of vcstocl_quirks.py since the
file is not intended to be directly executable.