[FEATURE ember-handlebars-compiler-ast-to-precompile] Revert.

Apparently, the changes in ember-handlebars-compiler were not needed.

I left the test in place (unflagged) to confirm we do not regress.
Merge pull request #5467 from rwjblue/remove-ast-precompile-feature

[FEATURE ember-handlebars-compiler-ast-to-precompile] Revert.