MAINT: Make useless imports of oldnumeric and numarray safe.

The oldnumeric and numarray packages were removed in numpy 1.9, but
some packages, e.g. scipy, import them even though they are not used.
This defines both to the string 'removed' in numpy/__init__.py, which
avoids an import error.
Merge pull request #3826 from charris/add-oldnumeric-numarray-to_init

MAINT: Make useless imports of oldnumeric and numarray safe.