gnu: Move sqlite to separate module.

gnu: Move sqlite to separate module.

* gnu/packages/databases.scm (sqlite, sqlite-3.26.0, sqlite-with-fts5,
sqlite-with-column-metadata): Move variables from here...
* gnu/packages/sqlite.scm: ...to this new module.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.
* gnu/packages/apl.scm,
gnu/packages/bittorrent.scm,
gnu/packages/calendar.scm,
gnu/packages/code.scm,
gnu/packages/crypto.scm,
gnu/packages/databases.scm,
gnu/packages/dc.scm,
gnu/packages/disk.scm,
gnu/packages/ebook.scm,
gnu/packages/education.scm,
gnu/packages/emacs.scm,
gnu/packages/emulators.scm,
gnu/packages/file-systems.scm,
gnu/packages/freedesktop.scm,
gnu/packages/ftp.scm,
gnu/packages/games.scm,
gnu/packages/geo.scm,
gnu/packages/gnome.scm,
gnu/packages/gnunet.scm,
gnu/packages/gnupg.scm,
gnu/packages/gnuzilla.scm,
gnu/packages/gps.scm,
gnu/packages/guile.scm,
gnu/packages/ibus.scm,
gnu/packages/kerberos.scm,
gnu/packages/kodi.scm,
gnu/packages/lisp.scm,
gnu/packages/mail.scm,
gnu/packages/messaging.scm,
gnu/packages/mpd.scm,
gnu/packages/music.scm,
gnu/packages/networking.scm,
gnu/packages/nfs.scm,
gnu/packages/ocaml.scm,
gnu/packages/package-management.scm,
gnu/packages/pdf.scm,
gnu/packages/photo.scm,
gnu/packages/php.scm,
gnu/packages/python.scm,
gnu/packages/qt.scm,
gnu/packages/ruby.scm,
gnu/packages/scheme.scm,
gnu/packages/sync.scm,
gnu/packages/syndication.scm,
gnu/packages/version-control.scm,
gnu/packages/video.scm,
gnu/packages/web-browsers.scm,
gnu/packages/webkit.scm: Adjust module references.