Delete unnecessary, outdated defconfigs
Previously, tuna_defconfig inherited properties from
android_4430_defconfig. Now, it containts everything it inherited
previously, so this is exactly the same config as before, but it's a lot
more easier to maintain this way.
Reduce frame buffer size
We only use about 10.5 megabytes, so 12MB should be more than enough.
This gives back 4 MB of wasted RAM.