BUG: Remove redundant arg _key

[Flying-Tom]

What do these changes do?

Remove redundant arg _key in _mars.core.base

Related issue number

Fixes #443

Check code requirements

• [x] tests added / passed (if needed)
• [x] Ensure all linting tests pass

[codecov[bot]]

Codecov Report

Merging #636 (125f7fe) into main (bc0c60c) will increase coverage by 0.03%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #636      +/-   ##
==========================================
+ Coverage   82.50%   82.54%   +0.03%     
==========================================
  Files        1025     1025              
  Lines       79377    79377              
  Branches    16443    16443              
==========================================
+ Hits        65491    65522      +31     
+ Misses      11627    11589      -38     
- Partials     2259     2266       +7     

Flag	Coverage Δ
unittests	82.41% <100.00%> (+0.03%)	:arrow_up:

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

Files Changed	Coverage Δ
python/xorbits/_mars/core/base.py	99.00% <100.00%> (ø)

... and 14 files with indirect coverage changes

[aresnow1]

Add a test to check the copied one is same as original.

[Flying-Tom]

A fix has been done in #709 so this one closed