[python] Drop extra index array schema name

[jp-dark]

Prevent extra index column from being added to pandas dataframe generated schema.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.79%. Comparing base (11d5396) to head (cb1fc54).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3033      +/-   ##
==========================================
+ Coverage   89.64%   89.79%   +0.15%     
==========================================
  Files          40       40              
  Lines        4096     4098       +2     
==========================================
+ Hits         3672     3680       +8     
+ Misses        424      418       -6     

Flag	Coverage Δ
python	89.79% <100.00%> (+0.15%)	⬆️

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

Components	Coverage Δ
python_api	89.79% <100.00%> (+0.15%)	⬆️
libtiledbsoma	∅ <ø> (∅)