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

@@ -162,29 +162,7 @@ Upgrade in place
 ~~~~~~~~~~~~~~~~
 
 If you are upgrading in place, you will need to shut down Cyrus
-entirely while you install the new package.  If your old installation
-was using Berkeley DB format databases, you will need to convert or
-upgrade the databases **before** you upgrade.  Cyrus v3.8 does not
-support Berkeley DB at all.
-
-.. note::
-
-    If you are upgrading from Cyrus version 2.5 or earlier,
-    and your system is configured with the following combination
-    in :cyrusman:`imapd.conf(5)`::
-
-        fulldirhash: yes
-        hashimapspool: either yes or no
-        unixhierarchysep: yes
-
-    then you will not be able to upgrade-in-place.  This is due to
-    a change in how directory hashes are calculated for users whose
-    localpart contains a dot, which was introduced in 3.0.0.  After
-    an in-place upgrade, Cyrus will not be able to find these users'
-    metadata and/or mailboxes.
-
-    If you have this configuration, you will need to upgrade by
-    replicating, not in place.
+entirely while you install the new package.
 
 Do What As Who?
 ###############
@@ -338,35 +316,7 @@ 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
 ---------------------------------