Revert "initrd: Add extract scripts"

This reverts commit 8177920f3696eb0c05b39a6f5bbe33a36c6566a5.
Revert "initrd: Add initrd.cpio"

This reverts commit fc27b3c6b17fed9fdbc38531f4b12733a8a9e9a7.
initrd: Use text device tree description instead of initrd.cpio binary

  - Get init from http://code.google.com/p/dingoo-linux/
  - Make a list of dirs and nods in initrd/tree.txt
  - Let kernel make initrd.cpio for us
defconfig: MIPS: JZ4750D: Use initrd/tree.txt instead of initrd.cpio