Delete old code

[felixwang9817]

What this PR does / why we need it: This PR deletes old code left over from previous Feast versions (Client, grpc, etc.).

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

Deletes Client

[codecov-commenter]

Codecov Report

Merging #1743 (6c94654) into master (2dfdace) will increase coverage by 4.87%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1743      +/-   ##
==========================================
+ Coverage   79.10%   83.97%   +4.87%     
==========================================
  Files          81       73       -8     
  Lines        6938     5996     -942     
==========================================
- Hits         5488     5035     -453     
+ Misses       1450      961     -489     

Flag	Coverage Δ
integrationtests	83.88% <ø> (+4.86%)	⬆️
unittests	64.15% <ø> (+2.21%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
sdk/python/feast/__init__.py	90.00% <ø> (-0.48%)	⬇️

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[felixwang9817]

/retest

[achals]

/lgtm

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: achals, felixwang9817

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