Handle Deprecation Of experimental_ref api

[NihalHarish]

Description of changes:

• experimental_ref API is being deprecated in favor of ref

Style and formatting:

I have run pre-commit install to ensure that auto-formatting happens with every commit.

Issue number, if available

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[codecov-commenter]

Codecov Report

Merging #356 into master will decrease coverage by 0.91%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #356      +/-   ##
==========================================
- Coverage   82.81%   81.90%   -0.92%     
==========================================
  Files          86       86              
  Lines        6478     6482       +4     
==========================================
- Hits         5365     5309      -56     
- Misses       1113     1173      +60     

Impacted Files	Coverage Δ
smdebug/tensorflow/keras.py	59.61% <0.00%> (-20.32%)	:arrow_down:
smdebug/core/singleton_utils.py	79.41% <0.00%> (-5.89%)	:arrow_down:
smdebug/tensorflow/tensor_ref.py	85.48% <0.00%> (-1.62%)	:arrow_down:
smdebug/core/json_config.py	95.93% <0.00%> (-0.82%)	:arrow_down:
smdebug/core/hook.py	91.66% <0.00%> (-0.80%)	:arrow_down:
smdebug/tensorflow/base_hook.py	75.39% <0.00%> (-0.80%)	:arrow_down:
smdebug/core/reductions.py	91.30% <0.00%> (ø)
smdebug/trials/trial.py	96.82% <0.00%> (+0.28%)	:arrow_up:
smdebug/core/utils.py	84.03% <0.00%> (+0.46%)	:arrow_up:
... and 10 more

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