svn commit: r78487 - dev/arrow/apache-arrow-21.0.0-rc4

[brycemecum]

Author: brycemecum
Date: Thu Jul 31 19:42:25 2025
New Revision: 78487

Log:
Remove old Apache Arrow RC: apache-arrow-21.0.0-rc4/

Deleted:
   dev/arrow/apache-arrow-21.0.0-rc4/