Remove list of times as on option for cutoff_time in calculate_feature_matrix

[rwedge]

Using a list of times for cutoff_time was creating some unexpected behavior if there wasn't an instance_ids list of the same length. Some examples:

ft.calculate_feature_matrix(features=features,
                            entityset=es,
                            instance_ids=[0, 1, 2],
                            cutoff_time=[0, 1])

This calculates features for instance 0 at time 0, instance 1 at time 1, and doesn't calculate features for instance 2.

ft.calculate_feature_matrix(features=features,
                            entityset=es,
                            instance_ids=[0, 1],
                            cutoff_time=[0, 1, 2])

This calculates features for instance 0 at time 0, instance 1 at time 1, and not use time 2.

ft.calculate_feature_matrix(features=features,
                            entityset=es,
                            cutoff_time=[0, 1])

This would calculate features for the first instance in the entity's dataframe at time 0 and calculate features for the second instance in the entity's dataframe at time 1.

While requiring a list of instance_ids with the same length as the list of cutoff times is one way to resolve this issue, equal length lists of instances and times can easily be represented in DataFrame format and would leave one less input case to handle.

[codecov-io]

Codecov Report

Merging #165 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #165      +/-   ##
==========================================
+ Coverage    92.9%   92.92%   +0.01%     
==========================================
  Files          72       72              
  Lines        7753     7785      +32     
==========================================
+ Hits         7203     7234      +31     
- Misses        550      551       +1

Impacted Files	Coverage Δ
...computational_backends/calculate_feature_matrix.py	97.87% <100%> (ø)	⬆️
...utational_backend/test_calculate_feature_matrix.py	99.58% <100%> (+0.02%)	⬆️
featuretools/utils/gen_utils.py	64.44% <0%> (-2.23%)	⬇️

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[kmax12]

Looks good to me!