Freeze columns only once per Result

Conflicts:
	activerecord/lib/active_record/result.rb
Revert "Merge pull request #8209 from senny/backport_8176"

This reverts commit 724020278480855bddfe749c91f1074d4f50f3c6, reversing
changes made to e4e2bcce75b85fb8c1c49509a17bd5dfe6034c32.

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/lib/active_record/relation/calculations.rb
	activerecord/test/cases/calculations_test.rb