package/mongodb: remove package

Fixes:
http://autobuild.buildroot.net/results/dd4/dd412fae45a84e44e7e6a49f8cdb124d0851c1df/

The mongodb version used (3.3.4) is no longer supported by upstream and
fails to build with openssl 1.1.1x.  On top of that it uses internal copies
of boost, pcre and zlib instead of the system ones.

Bumping the version to 3.4.19 (which is still supported until September
2019) has been tried, but it:

- No longer builds for 32bit ARM

- Doesn't build without extra patches, E.G.:
  https://git.openembedded.org/meta-openembedded/tree/meta-oe/recipes-support/mongodb/mongodb/0002-d_state.cpp-Add-missing-dependenncy-on-local_shardin.patch?h=rocko

- Doesn't build with the system version of boost (1.69.0)

- Also fails to build with openssl-1.1.1x

So it looks like mongodb needs to be bumped to the 3.6.x series (which
changes the license to the SSPL) - Or simply dropped.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

Config.in.legacy

@@ -207,6 +207,12 @@ config BR2_PACKAGE_GNURADIO_QTGUI
 	help
 	  The gr-qtgui option was removed.
 
+config BR2_PACKAGE_MONGODB
+	bool "mongodb package removed"
+	select BR2_LEGACY
+	help
+	  The mongodb package was removed.
+
 config BR2_PACKAGE_LUACRYPTO
 	bool "luacrypto package removed"
 	select BR2_LEGACY