Fix a few Sphinx warnings

This precludes us from landing anything in the gate, because we
treat Sphinx warnings as errors in OpenStack.

Specifically, 3 warnings are fixed:

/home/zuul/src/opendev.org/openstack/swift/swift/common/middleware\
/s3api/etree.py:docstring of\
 swift.common.middleware.s3api.etree.Element:1:\
Inline strong start-string without end-string.

duplicate object description of\
 swift.common.middleware.versioned_writes, other instance in\
 middleware, use :noindex: for one of them

duplicate object description of\
 swift.common.ring.composite_builder, other instance in\
 overview_ring, use :noindex: for one of them

Change-Id: I5e0bd61a301d46b2674b4605882462575b635220

doc/source/index.rst

@@ -53,7 +53,6 @@ Overview and Concepts
     overview_replication
     ratelimit
     overview_large_objects
-    overview_object_versioning
     overview_global_cluster
     overview_container_sync
     overview_expiring_objects

doc/source/middleware.rst

@@ -37,7 +37,7 @@ AWS S3 Api
     :show-inheritance:
 
 .. automodule:: swift.common.middleware.s3api.etree
-    :members:
+    :members: _Element
     :show-inheritance:
 
 .. automodule:: swift.common.middleware.s3api.utils

doc/source/overview_object_versioning.rst

@@ -1,5 +0,0 @@
-Object Versioning
-=================
-
-.. automodule:: swift.common.middleware.versioned_writes
-    :show-inheritance:

doc/source/overview_ring.rst

@@ -359,7 +359,8 @@ can't get perfect balance due to too many partitions recently moved).
 ---------------
 Composite Rings
 ---------------
-.. automodule:: swift.common.ring.composite_builder
+
+See :ref:`composite_builder`.
 
 **********************************
 swift-ring-composer (Experimental)

doc/source/ring.rst

@@ -24,6 +24,8 @@ Ring Builder
     :undoc-members:
     :show-inheritance:
 
+.. _composite_builder:
+
 Composite Ring Builder
 ======================