Remove DataFrame.quantiles from docs.

[bdice]

Description

Removes documentation for DataFrame.quantiles, which was deprecated and then removed in #12281. This issue was discovered while building the docs in #12592.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[ajschmidt8]

/merge

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (branch-23.04@3aab6b8). Click here to learn what that means.
Patch has no changes to coverable lines.

Additional details and impacted files

@@               Coverage Diff               @@
##             branch-23.04   #12684   +/-   ##
===============================================
  Coverage                ?   85.81%           
===============================================
  Files                   ?      158           
  Lines                   ?    25151           
  Branches                ?        0           
===============================================
  Hits                    ?    21584           
  Misses                  ?     3567           
  Partials                ?        0           

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