contrib: remove install_db4.sh

Now that we can build a bdb-only depends prefix, there is no need to
maintain a bdb-building bash script, that does the same things as
depends, except worse, as it's missing patches and workarounds. i.e #26623.

doc/build-openbsd.md

@@ -41,16 +41,18 @@ pkg_add sqlite3
 BerkeleyDB is only required to support legacy wallets.
 
 It is recommended to use Berkeley DB 4.8. You cannot use the BerkeleyDB library
-from ports. However you can build it yourself, [using the installation script included in contrib/](/contrib/install_db4.sh), like so, from the root of the repository.
+from ports. However you can build it yourself, [using depends](/depends).
 
 ```bash
-./contrib/install_db4.sh `pwd`
+gmake -C depends NO_BOOST=1 NO_LIBEVENT=1 NO_QT=1 NO_SQLITE=1 NO_NATPMP=1 NO_UPNP=1 NO_ZMQ=1 NO_USDT=1
+...
+to: /path/to/bitcoin/depends/x86_64-unknown-openbsd
 ```
 
 Then set `BDB_PREFIX`:
 
 ```bash
-export BDB_PREFIX="$PWD/db4"
+export BDB_PREFIX="/path/to/bitcoin/depends/x86_64-unknown-openbsd"
 ```
 
 #### GUI Dependencies