Bug 1576988 - [docs] Remove 'Indices and tables' section from doc trees, r=Standard8

The main motivation here is to get these subsections out of the main index.
While changing the heading to an 'h2' or lower would suffice, I opted to remove
them entirely. I did this because the links in this section is for the overall
global documentation. E.g, the "Indices and tables" section under /tools/lint,
has nothing to do with linting.

It is still possible to access the index and search page from the root:
https://firefox-source-docs.mozilla.org/#indices-and-tables

Differential Revision: https://phabricator.services.mozilla.com/D43653

--HG--
extra : moz-landing-system : lando

mobile/android/docs/index.rst

@@ -22,10 +22,3 @@ Contents:
    push
    gradle
    testcoverage
-
-Indices and tables
-==================
-
-* :ref:`genindex`
-* :ref:`modindex`
-* :ref:`search`

testing/mozbase/docs/index.rst

@@ -42,11 +42,3 @@ want to do then dive in!
    servingcontent
    loggingreporting
    devicemanagement
-
-Indices and tables
-==================
-
-* :ref:`genindex`
-* :ref:`modindex`
-* :ref:`search`
-

tools/lint/docs/index.rst

@@ -30,10 +30,3 @@ like mach, mozreview and taskcluster.
   linters/flake8
   linters/l10n
   linters/rstlinter
-
-Indices and tables
-==================
-
-* :ref:`genindex`
-* :ref:`modindex`
-* :ref:`search`