ksmbd: remove experimental warning

[ Upstream commit f5069159

 ]

ksmbd has made significant improvements over the past two
years and is regularly tested and used.  Remove the experimental
warning.

Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>