Revert benchmark helper regression. Use a #capture within a #benchmark
block. Breaks benchmark calls that return non-String values otherwise.

Revert "add benchmark helper that works in erb"

This reverts commit 904e544cc8f5846de7c31827bb5556c6a238c0de.

Conflicts:
	actionpack/lib/action_view/helpers.rb
	actionpack/lib/action_view/helpers/benchmark_helper.rb
	actionpack/test/template/benchmark_helper_test.rb