[operator] Fix reshape and mean

[barry-jin]

Description

Two issues:

1. Operator mean falls back to old api
2. Operator reshape falls back to old api as it occurs twice in mx.nd.np.all

>>> mx.nd.np.__all__
['shape', 'zeros', 'zeros_like', 'ones', 'ones_like', 'full', 'full_like', 'empty_like', 'invert', 'delete',
'add', 'broadcast_to', 'subtract', 'multiply', 'divide', 'mod', 'remainder', 'fmod', 'power',
'bitwise_not', 'trace', 'transpose', 'copy', 'moveaxis', 'reshape', 'dot', 'arctan2',
'sin', 'cos', 'tan', 'sinh', 'cosh', 'tanh', 'log10', 'sqrt', 'cbrt', 'abs', 'insert', 
'fabs', 'absolute', 'exp', 'expm1', 'arcsin', 'arccos', 'arctan', 'sign', 'log',
'degrees', 'log2', 'matmul', 'log1p', 'rint', 'radians', 'reciprocal', 'square',
'negative', 'fix', 'ceil', 'floor', 'histogram', 'trunc', 'logical_not', 'arcsinh',
'arccosh', 'arctanh', 'argsort', 'all', 'any', 'sort', 'tensordot', 'eye',
'linspace', 'median', 'tril_indices', 'triu_indices_from', 'triu_indices', 
'logspace', 'expand_dims', 'tile', 'arange', 'array_split', 'split', 'hsplit', 'vsplit', 
'dsplit', 'concatenate', 'append', 'stack', 'vstack', 'row_stack', 'column_stack', 
'hstack', 'dstack', 'average', 'mean', 'maximum', 
'fmax', 'minimum', 'fmin', 'around', 'round', 'round_', 'flatnonzero', 'max', 'min', 
'amax', 'amin', 'logical_and', 'logical_or', 'logical_xor', 'swapaxes', 'clip', 'argmax', 
'argmin', 'std', 'var', 'indices', 'copysign', 'ravel', 'unravel_index', 'diag_indices_from', 
'hanning', 'hamming', 'blackman', 'flip', 'flipud', 'fliplr', 'hypot', 'bitwise_and', 
'bitwise_xor', 'bitwise_or', 'rad2deg', 'deg2rad', 'unique', 'lcm', 'gcd', 
'tril', 'triu', 'tri', 'identity', 'take', 'ldexp', 'vdot', 'inner', 'outer', 'cross', 'kron', 
'equal', 'not_equal', 'greater', 'less', 'greater_equal', 'less_equal', 'roll', 'rot90', 
'einsum', 'true_divide', 'nonzero', 'quantile', 'percentile', 'shares_memory', 
'may_share_memory', 'interp', 'diff', 'ediff1d', 'resize', 'polyval', 'nan_to_num', 
'isnan', 'isinf', 'isposinf', 'isneginf', 'isfinite', 'atleast_1d', 'atleast_2d', 'atleast_3d', 
'fill_diagonal', 'squeeze', 'where', 'bincount', 'rollaxis', 'diagflat', 'repeat', 'prod', 
'pad', 'cumsum', 'sum', 'diag', 'diagonal', 'product', 'reshape', 'sometrue']

Checklist

Essentials

• PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented

Changes

• Feature1, tests, (and when applicable, API doc)
• Feature2, tests, (and when applicable, API doc)

Comments

• If this change is a backward incompatible change, why must this change be made.
• Interesting edge cases to note here

[mxnet-bot]

Hey @barry-jin , Thanks for submitting the PR
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[barry-jin]

@mxnet-bot run ci [centos-cpu]

[mxnet-bot]

Jenkins CI successfully triggered : [centos-cpu]