lei: drop coderepo placeholders, submodule TODO

lei: drop coderepo placeholders, submodule TODO

"lei blob" supports --git-dir and -C, and checks if the
current directory has a git directory associated with it.
It will likely support submodules in the future.

I'm inclined to believe declaring coderepos in a command-line
tool is needless clutter and users will rarely want to search
for blobs across different projects when on the command-line.