Revert "i2c-tools: Add i2c-dev.h to staging directory for userspace i2c drivers."

Revert "i2c-tools: Add i2c-dev.h to staging directory for userspace i2c drivers."

This reverts commit ff673f9a22b1467878f1a117f2c6198e9683d5c7, as the
modified i2c-dev.h from i2c-tools has some definitions that conflict
with the i2c.h from the kernel headers. This means that a userspace
program or library that includes both will fail to build, as is the
case with libsoc.

Fixes:

  http://autobuild.buildroot.org/results/1f4/1f451a338487a2a3c8a8f9b18540d41b90ee5aac/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>