config: Remove KERNEL_GIT_LOCAL_REPOSITORY option

The GIT_LOCAL_REPOSITORY option adds the --reference argument to the
git clone kernel command line, if KERNEL_GIT_CLONE_URI is set.

This option is intended to speed-up the repo creation by using local
objets rather than downloading it. However, a local repo can be cloned
much faster by setting GIT_LOCAL_REPOSITORY directly to the local tree.

In that case, git clone will bypass the normal "git aware" transport
mechanism and clone the repository by copying and hardlinking objects
rather than downloading it, resulting in a significant speed increase.

That makes the GIT_LOCAL_REPOSITORY option pretty useless so we'll just
remove it and recommand the usage of KERNEL_GIT_CLONE_URI directly.

Signed-off-by: Mathieu Olivari <mathieu@qca.qualcomm.com>

SVN-Revision: 40944