Remove "sql connection" backwards compatability for database

In 4.0 we deprecated connections using the "sql" driver in favor of
using the new "database" config file section.  Remove the backwards
compatible handling of that so that "sql" connections or lack of
"database" section report an error.

Change-Id: I7e592cf5ff63f73f487e41bb6e3e4a4ae523e3fc

releasenotes/notes/last3x-8682ada4910fa750.yaml

@@ -13,7 +13,7 @@ prelude: |
   These features are supported now, so it is important that you take
   this time to :ref:`switch your ZooKeeper connection to use
   TLS<zk-encrypted-connections>`, and :ref:`configure a SQL
-  connection<sql-driver>`.  Even though only some Zuul components
+  connection<database>`.  Even though only some Zuul components
   connect to ZooKeeper today, you should ensure that the
   ``[zookeeper]`` section is present in ``zuul.conf`` for all
   components, and that they have network connectivity to the ZooKeeper

releasenotes/notes/postgres-ae4f8594d0f4b256.yaml

@@ -2,4 +2,4 @@
 features:
   - |
     PostgreSQL is now officially supported as database backend.
-    See :attr:`<sql connection>` on how to configure database connections.
+    See ``sql connection`` on how to configure database connections.

releasenotes/notes/report-build-page-2-49088c2b0a36e1b7.yaml

@@ -3,7 +3,7 @@ features:
   - |
     An option to use the URL of the Zuul build page when reporting has
     been added.  This feature requires that all the pipelines in the
-    tenant have a :ref:`SQL reporter<sql_reporter>` configured, and at
+    tenant have a SQL reporter configured, and at
     least one of :attr:`tenant.web-root` or :attr:`web.root` must be
     defined.
 

releasenotes/notes/required-sql-7dd38b76d9f4273f.yaml

@@ -8,5 +8,5 @@ upgrade:
 
 deprecations:
   - |
-    Defining database connections using :attr:`<sql connection>` is now
+    Defining database connections using sql connection is now
     deprecated. Refer to :ref:`database` how to configure the database now.

releasenotes/notes/sql-connection-removal-8579399ab165abf9.yaml

@@ -0,0 +1,7 @@
+---
+upgrade:
+  - |
+    Support for configuring the database as a `connection` in
+    ``zuul.conf`` was deprecated in Zuul version 4.0 and has now been
+    removed.  Refer to :ref:`database` how to configure the database
+    now.

releasenotes/notes/version-table-prefix-c6a5e84851268f4d.yaml

@@ -2,7 +2,7 @@
 upgrade:
   - |
     The alembic version table is fixed to being prefixed too. This is necessary
-    when using :attr:`<sql connection>.table_prefix`. However if you are
+    when using ``table_prefix``. However if you are
     already using ``table_prefix`` you will need to rename the table
     ``alembic_version`` to ``<prefix>alembic_version`` before starting Zuul.
     Otherwise zuul will try to create the tables again and fail. If you're not