Remove type annotation
# What does this PR do ?

Remove type annotations in the `calc_length` function since it causes errors when scripting Conformer models.

**Collection**: ASR

This is the error:

```
[NeMo E 2022-08-03 11:47:46 exportable:116] jit.script() failed!\
    Variable 'add_pad' is annotated with type float but is being assigned to a value of type Tensor:
      File "/Users/allabana/.virtualenvs/meval/lib/python3.8/site-packages/nemo/collections/asr/parts/submodules/subsampling.py", line 149
    def calc_length(lengths, padding, kernel_size, stride, ceil_mode, repeat_num=1):
        """ Calculates the output length of a Tensor passed through a convolution or max pooling layer"""
        add_pad: float = (padding * 2) - kernel_size
        ~~~~~~~ <--- HERE
        one: float = 1.0
        for i in range(repeat_num):
```

This is an example usage that causes the error:

```py
pre_trained_model_name = "stt_en_conformer_ctc_small"
model = EncDecCTCModelBPE.from_pretrained(pre_trained_model_name, map_location='cpu')
model.eval()
model.export(f"/tmp/{model._get_name()}.ts", check_trace=True, try_script=True)
```

# Changelog 
- Remove type annotations for `add_pad`/`one` in `nemo.collections.asr.parts.submodules.subsampling.calc_length`
- Add type annotations to `calc_length` method args.

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**Pre checks**:
- [ ] Make sure you read and followed [Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md)
- [ ] Did you write any new necessary tests?
- [ ] Did you add or update any necessary documentation?
- [ ] Does the PR affect components that are optional to install? (Ex: Numba, Pynini, Apex etc)
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**PR Type**:
- [ ] New Feature
- [X] Bugfix
- [ ] Documentation

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