config: Drop Solaris UID/GID note

The note is from 7c9daeb (Introducing Solaris in OCI, 2016-04-25,
opencontainers#411), but as I pointed out there [1], this is also true for Linux.
08908d6 (config: Explicit container namespace for uid, gid, and
additionalGids, 2016-04-29, opencontainers#412) landed in parallel with more
explicit namepacing for these fields, so we no longer need the
overly-specific Solaris note.

[1]: opencontainers#411 (comment)

Signed-off-by: W. Trevor King <[email protected]>

Author: wking

config.md

@@ -160,8 +160,6 @@ For Linux and Solaris based systems the user structure has the following fields:
 
 _Note: symbolic name for uid and gid, such as uname and gname respectively, are left to upper levels to derive (i.e. `/etc/passwd` parsing, NSS, etc)_
 
-_Note: For Solaris, uid and gid specify the uid and gid of the process inside the container and need not be same as in the host._
-
 ### Example (Linux)
 
 ```json