revert: "fix($compile): render nested transclusion at the root of a template"

This reverts commit 6d1e7cdc51c074139639e870b66997fb0df4523f.

This commit was causing breakages because of its assumption that transcluded
content would be handled predictably, i.e. with ngTransclude, whereas many
use cases involve manipulating transcluded content in linking functions.