doc: Remove user guide links from "Modules" section

These are duplicate links and they really are user guides, so remove
them from the modules section.

Change-Id: I0d3bdc235c75f9faa2501984db812dd525cf4fc2
Signed-off-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-on: https://review.gerrithub.io/397634
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Dariusz Stojaczyk <dariuszx.stojaczyk@intel.com>
Reviewed-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>

doc/index.md

@@ -18,9 +18,9 @@
 
 # User Guides {#user_guides}
 
-- @ref iscsi_getting_started
-- @ref nvmf_getting_started
-- @ref blobfs_getting_started
+- @ref iscsi
+- @ref nvmf
+- @ref blobfs
 - @ref jsonrpc
 
 # Programmer Guides {#general}
@@ -33,14 +33,10 @@
 
 # Modules {#modules}
 
-
 - @ref nvme
-- @ref nvmf
 - @ref ioat
-- @ref iscsi
 - @ref bdev
 - @ref blob
-- @ref blobfs
 - @ref vhost
 - @ref virtio