Revert "requirements-swh*: add dependencies on swh-scanner"

... for the time being, as swh.scanner is not published on PyPI yet

This reverts commit bdefee74.

requirements-swh-dev.txt

@@ -20,4 +20,3 @@
 -e ../swh-vault
 -e ../swh-web
 -e ../swh-web-client
--e ../swh-scanner

requirements-swh.txt

@@ -11,7 +11,6 @@ swh.loader.mercurial
 swh.loader.svn
 swh.model
 swh.objstorage[testing]
-swh.scanner
 swh.scheduler
 swh.storage[schemata,listener]
 swh.vault