win32: remove automatic build option from mingw script

win32: remove automatic build option from mingw script

This removes the "Do you want to checkout and build Clutter?" option
from the mingw-cross-compile.sh script and renames the script
mingw-fetch-dependencies.sh

As it stands the mingw-cross-compile.sh script isn't enough to fetch all
the dependencies for building clutter, since Tor doesn't provide binaries
for json-glib so the option to checkout and build clutter can't work.

Also it doesn't seem ideal to clone a fresh clutter repo instead of
being able to compile the source of the current repo.