Don't add Imputer to make_pipeline if no numeric / categorical columns

[angela97lin]

Closes #1938

[codecov]

Codecov Report

Merging #1967 (a056dae) into main (80267d7) will increase coverage by 0.1%.
The diff coverage is 100.0%.

@@            Coverage Diff            @@
##             main    #1967     +/-   ##
=========================================
+ Coverage   100.0%   100.0%   +0.1%     
=========================================
  Files         273      273             
  Lines       22339    22391     +52     
=========================================
+ Hits        22333    22385     +52     
  Misses          6        6             

Impacted Files	Coverage Δ
evalml/pipelines/utils.py	100.0% <100.0%> (ø)
evalml/tests/pipeline_tests/test_pipeline_utils.py	100.0% <100.0%> (ø)

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[freddyaboulton]

@angela97lin This looks good to me!

[angela97lin]

@freddyaboulton Dang, you're speedymcspeedster at reviewing! 😂
I didn't even realize I made it a non-draft PR, thanks a lot! 🥳