build: don't check for deprecated berkeley-db4 package

Fixes:
```bash
checking for brew... brew
Warning: Use berkeley-db@4 instead of deprecated berkeley-db4
```

.cirrus.yml

@@ -284,7 +284,7 @@ task:
 task:
   name: 'macOS 11 native [gui] [no depends]'
   brew_install_script:
-    - brew install boost libevent berkeley-db4 qt@5 miniupnpc libnatpmp ccache zeromq qrencode sqlite libtool automake pkg-config gnu-getopt
+    - brew install boost libevent berkeley-db@4 qt@5 miniupnpc libnatpmp ccache zeromq qrencode sqlite libtool automake pkg-config gnu-getopt
   << : *GLOBAL_TASK_TEMPLATE
   osx_instance:
     # Use latest image, but hardcode version to avoid silent upgrades (and breaks)

configure.ac

@@ -683,8 +683,8 @@ case $host in
          dnl It's safe to add these paths even if the functionality is disabled by
          dnl the user (--without-wallet or --without-gui for example).
 
-         if test "x$use_bdb" != xno && $BREW list --versions berkeley-db4 >/dev/null && test "x$BDB_CFLAGS" = "x" && test "x$BDB_LIBS" = "x"; then
-           bdb_prefix=$($BREW --prefix berkeley-db4 2>/dev/null)
+         if test "x$use_bdb" != xno && $BREW list --versions berkeley-db@4 >/dev/null && test "x$BDB_CFLAGS" = "x" && test "x$BDB_LIBS" = "x"; then
+           bdb_prefix=$($BREW --prefix berkeley-db@4 2>/dev/null)
            dnl This must precede the call to BITCOIN_FIND_BDB48 below.
            BDB_CFLAGS="-I$bdb_prefix/include"
            BDB_LIBS="-L$bdb_prefix/lib -ldb_cxx-4.8"