core: Remove last remaining android customization of mupen64plus-core.

We are now using a completely stock mupen64plus core.  Once Richard
approves the pull request below, then we can safely use the head revi-
sion of mupen64plus-core without any modification.

https://bitbucket.org/richard42/mupen64plus-core/pull-request/62/remove-unneeded-include-in-screenshotcpp/diff
ae-bridge: Add screenshot command to JNI.

I wasn't actually able to capture any screenshots with this (just black
images)... but I'll commit it anyhow in case another dev wants to make
it work.  Would definitely be useful, so that we can attach screenshots
to state-saves in version 3.  Also could make bug reporting a little
easier for the masses.

If you do want to try to get this working, be sure to specify a valid
target directory in CoreInterface.syncConfigFiles().