Strip the protocol from the path in LocalFileSystem.lexists

[LuisFigueroaG]

LocalFileSystem.lexists passes the path straight to os.path.lexists, so unlike the other methods it doesn't handle file:///local:// URLs:

>>> fs = fsspec.filesystem("file")
>>> fs.exists("file:///tmp/afile"), fs.lexists("file:///tmp/afile")
(True, False)

It now uses _strip_protocol, like chmod since #2218. The new test fails on master.