doc: remove obsolete v1 changes/porting docs

doc/kernel/overview/changes.rst contains information about changes from
kernel release 1.5 ("Version 1 Kernel") to the combined "Version 2
Kernel" and doc/porting/application.rst talked about how to change
applications using Version 1 interfaces to the Version 2 interface.
This information remains in the online tagged versions of the
documentation, but it's time to remove this from the current
documentation set. (Also removing example porting code.)

Fixes issue #1524

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>