lib/berkeley-db-1.xx: Update submodule URL and version.

This updates the berkeley-db-1.xx submodule URL to a repository hosted
under the micropython organisation, and makes the following changes:

- Moves the berkeley-db header files to a single directory within the
  submodule, and references all these headers with a much fuller path,
  which prevents symbol clashes (eg with esp32 and queue.h).

- Removes unused/non-working files from berkeley-db, which removes all
  symlinks in that repo (symlinks don't play well under Windows).

- Allows injecting an external configuration header into berkeley-db, so
  the configuration doesn't have to be provided by -Dxx=yy flags to the
  compiler (and possibly clashing with other symbols).

- Removes the advertising clause from the BSD 4-clause license of
  berkeley-db (see relevant commit and README.Impt.License.Change for
  details).

Signed-off-by: Damien George <damien@micropython.org>

.gitmodules

@@ -9,7 +9,7 @@
 	url = https://github.com/lwip-tcpip/lwip.git
 [submodule "lib/berkeley-db-1.xx"]
 	path = lib/berkeley-db-1.xx
-	url = https://github.com/pfalcon/berkeley-db-1.xx
+	url = https://github.com/micropython/berkeley-db-1.xx
 [submodule "lib/stm32lib"]
 	path = lib/stm32lib
 	url = https://github.com/micropython/stm32lib