Revert "documentation regarding after_validation"

This reverts commit c24aa2f2.

[#4653 state:resolved]
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

say something about after_(commit|rollback) in callbacks.rb, the fact that their implementation is elsewhere is not important for rdoc purposes

Signed-off-by: NRizwan Reza <rizwanreza@gmail.com>

Signed-off-by: NYehuda Katz <wycats@Yehuda-Katz.local>

Signed-off-by: NJoshua Peek <josh@joshpeek.com>

Changed ActiveRecord to use new callbacks and speed up observers by only notifying events that are actually being consumed.
Signed-off-by: NJoshua Peek <josh@joshpeek.com>

Break up DependencyModule's dual function of providing a "depend_on" DSL and "included" block DSL into separate modules. But, unify both approaches under AS::Concern.

Fixed broken after_save callback; was being called when before_create was canceled or before_update was canceled
Signed-off-by: NMichael Koziarski <michael@koziarski.com>
[#1735 state:committed]