Don't install sudo wrapper scripts

We can use the real binaries now thanks to the device driver.

I also added a new environment variable, EPIPHANY_XML, to setup.*sh.
The e-server wrapper script defined this variable and gave it as an
argument to the e-server binary. Since we can't rely on that anymore, I
think defining it as an environment variable the e-server can check for
is the best solution.

Also see companion pull request in epiphany-libs
adapteva/epiphany-libs#27