Clean up and standardize landing pages

doc index.rst:
1. Update intro sentence to read as a complete sentence
2. Remove unused toctree
3. Correct heading levels (impacting side nav and correct rendering
of content)
4. Remove "Indices and Tables" section: genindex page not used,
search searches only index (not useful here)

releasenotes index.rst:
1. Remove search (make consistent with other openstack release note
pages)

Story: 2004737
Task: 29273

Change-Id: Iff659b42ab14ef5726869d9c9aa69b7c58a756fd
Signed-off-by: Kristal Dale <kristal.dale@intel.com>

doc/source/index.rst

@@ -1,11 +1,10 @@
+========================
 stx-update Documentation
 ========================
 
-StarlingX Installation/Update/Patching/Backup/Restore
-
-.. toctree::
-   :maxdepth: 2
-   :caption: Contents:
+The StarlingX stx-update project provides software patch
+(bug fix) management and deployment, as well as software release upgrade
+management.
 
 Release Notes
 -------------
@@ -24,7 +23,7 @@ API Reference
    API Reference <https://docs.starlingx.io/api-ref/stx-update>
 
 Links
-=====
+-----
 
 * Source: `stx-update`_
 * Code Review: `Gerrit`_
@@ -33,9 +32,3 @@ Links
 .. _stx-update: https://git.starlingx.io/cgit/stx-update/
 .. _Gerrit: https://review.openstack.org/#/q/project:openstack/stx-update
 .. _Storyboard: https://storyboard.openstack.org/#!/project/openstack/stx-update
-
-Indices and Tables
-==================
-
-* :ref:`search`
-* :ref:`genindex`

releasenotes/source/index.rst

@@ -6,8 +6,3 @@ stx-update Release Notes
    :maxdepth: 2
 
    unreleased
-
-Search
-------
-
-:ref:`search`