upgrade.rst: remove instructions for upgrades before 3.2

The only way to upgrade to 3.6 is to have first version 3.2 installed.
That said, it can be assumed that users will first read the upgrade
instructions to version 3.2 from https://www.cyrusimap.org/3.2/imap/download/upgrade.html .

Since there is stated already that BDB is gone in Cyrus IMAP 3.0 and the
handling of special-use flags after 2.4 is discussed, there is no need to
have this information in the upgrade notes for 3.6, 3.8 and master/dev .

docsrc/imap/download/upgrade.rst

@@ -338,35 +338,7 @@ DAEMON section.
 6. Upgrade specific items
 -------------------------
 
-* Special-Use flags
-
-   If your 2.4 :cyrusman:`imapd.conf(5)` made use of the ``xlist-XX``
-   directive(s), you can convert these to per-user special-use annotations
-   in your new install with the :cyrusman:`cvt_xlist_specialuse(8)` tool
-
-.. warning::
-
-    **Berkeley db format no longer supported since 3.0**
-
-    If you have any databases using Berkeley db, they'll need to be
-    converted to skiplist or flat *in your existing installation*. And
-    then optionally converted to whatever final format you'd like in
-    your 3.8 installation.
-
-    Databases potentially affected: mailboxes, annotations, conversations,
-    quotas.
-
-    On old install, prior to migration::
-
-       cvt_cyrusdb /<configdirectory>mailboxes.db berkeley /tmp/new-mailboxes.db skiplist
-
-    If you don't want to use flat or skiplist for 3.5, you can use
-    :cyrusman:`cvt_cyrusdb(8)` to swap to new format::
-
-       cvt_cyrusdb /tmp/new-mailboxes.db skiplist /<configdirectory>/mailboxes.db <new file format>
-
-.. note::
-    The :cyrusman:`cvt_cyrusdb(8)` command does not accept relative paths.
+* None
 
 7. Start new 3.8 Cyrus and verify
 ---------------------------------