Raise an error if user tries to call an omniscidb decorated function from python

[guilhermeleobas]

The following should fail:

@omnisci('int64(int64)')
def incr(a):
    return a + 1

incr(3)

At the moment, it is calling the RemoteJIT.__call__ function.

[tupui]

Duplicate of #400 no?

[guilhermeleobas]

Yes! I didn't see it when I opened this PR. Closing it