Don't try to install mod_tile.so using debian/libapache2-mod-tile.install

I tried to build a Debian package on Debian Wheezy, but this failed since mod_tile.so was not found in the expected location during the package build. I think that this was not working anymore since 273973e which moved the sources to a src/ directory in order to clean up the top level directory. However, debian/rules already contains calls to 'make' which install mod_tile.so to the correct location, so it's not even necessary to install it using debian/libapache2-mod-tile.install. This patch removes this line from libapache2-mod-tile.install which fixed the package build for me.