kernel: Eliminate use of KERNEL_V2 configuration option

The unified kernel is now the only supported kernel, so this
option is unnessary. Eliminating this option also enables
the removal of some legacy code that is no longer required.

Change-Id: Ibfc339d643c8de16a2ed2009c9b468848b8b4972
Signed-off-by: Allan Stephens <allan.stephens@windriver.com>