This reverts commit 09682e9e.

Conflicts:
	guides/source/en/association_basics.md

REASON: Translation work can not be done in the docrails repository

This reverts commit f5b9ed4f.

REASON: Translation work can not be done in the docrails repository

This note came about due to discussion in #6786.

I've personally seen too many newbies get this wrong and pluralize the association

This reverts commit 8cb94604.

Reason: #7377 was merged and it fixes this behavior.

Fixed bug in the example code. A bit related to rails issue in
 https://github.com/rails/rails/issues/3223

* Use right example for has_many :find method;
* Reword has_many :counter_sql doc notes.

This works just fine, is less code, and reduces the risk of someone implementing a SQL injection vulnerability.

The association guide previously recommended using a trick with single
quote delaying of string interpolation in order to handle setting association
conditions that would be evaluated at runtime. Using a proc is the new way as
this no longer works.