Remove featuretools install command

[kmax12]

We added a featuretools install command in #326 to allow installation of additional primitives. However, we now have a better way to do it using entry points implemented in #452. This PR removes the first way we implemented and keeps the new way only.

[codecov]

Codecov Report

Merging #475 into master will decrease coverage by 0.07%.
The diff coverage is 94.73%.

@@            Coverage Diff             @@
##           master     #475      +/-   ##
==========================================
- Coverage    96.3%   96.23%   -0.08%     
==========================================
  Files         103      100       -3     
  Lines        8882     8607     -275     
==========================================
- Hits         8554     8283     -271     
+ Misses        328      324       -4

Impacted Files	Coverage Δ
featuretools/primitives/api.py	100% <ø> (ø)	⬆️
featuretools/synthesis/__init__.py	100% <ø> (ø)	⬆️
featuretools/__main__.py	0% <0%> (-80%)	⬇️
featuretools/__init__.py	66.66% <100%> (ø)	⬆️
...ools/tests/primitive_tests/test_primitive_utils.py	100% <100%> (ø)
featuretools/primitives/utils.py	96.47% <92.68%> (-3.53%)	⬇️

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[rwedge]

Looks good to me