MAINT: remove scipy.io.save_as_module

In 0.11.0 we deprecated save_as_module and promised to remove it in0.12.0. This PR removes it.

This PR also moves the (private) dumbdbm_patched and dumb_shelve helper modules into weave, which still uses them.

Unfortunately, it seems `scipy.weave.catalog` (namely, `test_catalog.TestCatalog.test_add_function_persistent1`) fails for some reason when using Python's shelve module with the dumbdbm backend. So we can't get rid of the patched version at this time.