drop vendor directories from .gitignore
drop vendor directories from .gitignore

Prior to this change, the execnet vendoring directories were hidden from
Git. This could lead to the vendor'd execnet still being published from
old Git clones (in fact this happened for the 0.0.30 release on PyPI).

Drop the .gitignores to make it more obvious that we need to clean up
these files.

ceph/remoto,alfredodeza/remoto