vbox_x86: update init.vbox_x86.rc, remove custom init.rc

-- remove local copy of init.rc (start using system/core/rootdir/init.rc)
-- sync init.vbox_x86.rc with init.goldfish.rc (at SHA
   a503456526359767ffb383a06835308f62172dde)
-- Make the following changes:
   a) add mount calls
   b) remove call to init.goldfish.sh
   c) enable service netcfg
-- inherit frameworks/native/build/phone-xhdpi-1024-dalvik-heap.mk

Change-Id: Ic5f6b2da32dc79de85f3d7b93dffb483e480e098
Signed-off-by: Iliyan Malchev <malchev@google.com>