Drop version option from mount command

Fun fact: in protocol version negotiation, our 9p version must be
written "9P2000.L". In the 'version' mount option, it must be
written "9p2000.L". Very consistent!

The mount command as given complains about an unknown protocol
version. Drop it entirely because Linux defaults to 9p2000.L
anyways.

PiperOrigin-RevId: 202971961
Change-Id: I5d46c83f03182476033db9c36870c68aeaf30f65

Author: prattmic

pkg/p9/local_server/local_server.go

@@ -18,7 +18,7 @@
 //     local_server /tmp/my_bind_addr
 //
 // Then, connect using the Linux 9P filesystem:
-//     mount -t 9p -o trans=unix,version=9P2000.L /tmp/my_bind_addr /mnt
+//     mount -t 9p -o trans=unix /tmp/my_bind_addr /mnt
 //
 // This package also serves as an examplar.
 package main