Revert "Merge pull request #12443 from arthurnn/add_inverse_of_add_target"

This reverts commit 7ed5bdc834479c39e3b0ad5a38bcffe27983c10d, reversing
changes made to 31c79e291f42b1d862df06c552fe002864aae705.

Reason: this caused a regression when the associated record is creted in
a before_create callback.

See https://github.com/rails/rails/pull/12413#issuecomment-25848163
Revert "Merge pull request #12413 from arthurnn/inverse_of_on_build"

This reverts commit ccd11d58910059f07b28cc518dbdad42cbc8ea0c, reversing
changes made to 54c05acdba138f3a7a3d44dfc922b0fe4e4cf554.

Reason: This caused a regression when the associated record is created
in a before_create callback. See
https://github.com/rails/rails/pull/12413#issuecomment-25848163