games-rpg/grimrock: Bump to 20150707, EAPI 6, no bundling

games-rpg/grimrock: Bump to 20150707, EAPI 6, no bundling

This previously bundled SDL 2, probably because it wasn't packaged
when this was first added. With that unbundled, there are far fewer
dependencies and this makes unbundling everything less likely to
break. SDL is particularly stable in this regard. Because of this and
in the interests of security, I have dropped the bundled-libs
flag. Anyone experiencing issues can obviously file a bug report.

I swapped the wrapper script for a symlink as the latter works fine.

I dropped the message about libtxc_dxtn because this is no longer
necessary with recent versions of Mesa.

Package-Manager: Portage-2.3.24, Repoman-2.3.6