Remove reference to nonexistent CONFIG_UID_NS

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)

docs/sources/installation/kernel.rst

@@ -136,7 +136,6 @@ Namespaces:
 - CONFIG_NAMESPACES
 - CONFIG_UTS_NS
 - CONFIG_IPC_NS
-- CONFIG_UID_NS
 - CONFIG_PID_NS
 - CONFIG_NET_NS