Fix result print for SamplingVQE & QAOA - fixes #58

[woodsp-ibm]

Summary

Fixes #58.

Simply removes the overriden __str__ method in the sampling result class so conversion to string is done by the parent AlgorithmResult (as it done for all other results so it makes things consistent too).

Longer terms the change proposed in #53 will change things up by using dataclass so the result string format is wanted to be improved, maybe include a capability for just including the common fields or whatever things can be revisited at that point.

Details and comments

Was

>>> res = SamplingVQEResult()
>>> print(res)
SamplingMinimumEigensolverResult:
        Eigenvalue: None
        Best measurement
: None

Now

>>> res = SamplingVQEResult()
>>> print(res)
{   'aux_operators_evaluated': None,
    'best_measurement': None,
    'cost_function_evals': None,
    'eigenstate': None,
    'eigenvalue': None,
    'optimal_circuit': None,
    'optimal_parameters': None,
    'optimal_point': None,
    'optimal_value': None,
    'optimizer_evals': None,
    'optimizer_result': None,
    'optimizer_time': None}

[coveralls]

Pull Request Test Coverage Report for Build 5953737313

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.05%) to 90.038%

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Totals
Change from base Build 5953372270:	0.05%
Covered Lines:	6444
Relevant Lines:	7157

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💛 - Coveralls

[ElePT]

I know that @Cryoris's original motivation to override the __str__ method was not to overload the users with non-relevant outputs that "blow-up" exponentially with the number of qubits. I see his point there. At the same time, I think that it would make sense to expose outputs such as the optimal point, and that it is not ideal to have such a specific override of an else-general format among algorithms. Given that this very specific override might be confusing to some users, and that exceptions are harder to keep up with/ maintain, I believe the best way to go here is to merge this PR, but I am open to future refactorings of AlgorithmResult to improve readability of the converted string.