Remove sandbox command

[pingsutw]

TL;DR

The sandbox command has already been deprecated for a while; we can remove it now.

Type

• [ ] Bug Fix
• [ ] Feature
• [ ] Plugin

Are all requirements met?

• [ ] Code completed
• [ ] Smoke tested
• [ ] Unit tests added
• [ ] Code documentation added
• [ ] Any pending items have an associated Issue

Complete description

How did you fix the bug, make the feature etc. Link to any design docs etc

Tracking Issue

NA

Follow-up issue

NA

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (9c87165) 67.69% compared to head (659723f) 67.66%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #462      +/-   ##
==========================================
- Coverage   67.69%   67.66%   -0.03%     
==========================================
  Files         148      143       -5     
  Lines        6639     6575      -64     
==========================================
- Hits         4494     4449      -45     
+ Misses       1855     1841      -14     
+ Partials      290      285       -5     

Flag	Coverage Δ
unittests	67.66% <ø> (-0.03%)	:arrow_down:

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[pmahindrakar-oss]

@pingsutw We should probably move the references in flyte repo before removing this command from flytectl https://github.com/search?q=repo%3Aflyteorg%2Fflyte%20%22flytectl%20sandbox%22&type=code

[pingsutw]

https://github.com/flyteorg/flyte/pull/5034