git-p4 shouldn't attempt to store symlinks in LFS

git-p4 shouldn't attempt to store symlinks in LFS

git-p4.py would attempt to put a symlink in LFS if its file extension
matched git-p4.largeFileExtensions.

Git LFS doesn't store symlinks because smudge/clean filters don't handle
symlinks. They never get passed to the filter process nor the
smudge/clean filters, nor could that occur without a change to the
protocol or command-line interface. Unless Git learned how to send them
to the filters, Git LFS would have a hard time using them in any useful
way.

Git LFS's goal is to move large files out of the repository history, and
symlinks are functionally limited to 4 KiB or a similar size on most
systems.

Signed-off-by: Matthew McClain <mmcclain@noprivs.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>