Add functionality for removing zero extent loops in the RemovNoOp pass

[umangyadav]

Consider the following example:

def test_generate_zero_extent_loop():
    ib = tvm.ir_builder.create()
    m = tvm.var('m')
    n = tvm.var('n')
    with ib.for_range(0, 16, "i") as i:
        with ib.if_scope(ib.likely(i>0)):
            with ib.if_scope(ib.likely(i<7)):
                ib.emit(tvm.make.Evaluate(m))

    stmt = ib.get()
    print("==================================")
    print(stmt)
    stmt = tvm.ir_pass.LoopPartition(stmt, True)
    print("==================================")
    print(stmt)
    stmt = tvm.ir_pass.Simplify(stmt)
    print("==================================")
    print(stmt)

In this case, LoopPartition gives the following output after the Simplify pass:

0
for (i, 0, 6) {
  m
}
for (i, 0, 0) {
  m
}
for (i, 0, 9) {
  0
}

Dead zero extent loops can be removed from RemoveNoOp pass if functionality for that is added.