Revert "[FIX] models: make `onchange` return a smaller diff"

This reverts commit 2054b5928574affbb7efcd8a9ab146ee4fa34938 which
already has been fixed multiple times [0].

However this change does not correctly handle successive onchange calls on
ony2many fields which alter existing rows.

i.e., in saas~11.4, an onchange has been added on move lines [1] in
order to create and/or update lines containing taxes amounts.
However, with diff-only onchange, a second call to onchange will discard
changes made by a first one as nothing change between the 2 calls.

Scenario: On an existing account.move, add a new credit line with a tax set.
The first onchange will update the tax line with new amount. Add a
second line (with debit amount balanced). The onchange will not change
the tax line, resulting as it value being reset to initial value. As a
result, the move is not balanced and cannot be saved.

[0] cd2ccc4110274e23607521c18309f07cca68476a, 5e58ac16c3cae2d5c45e7c9f746ed810b835a65d, 07023137cd17d8917673fd6ba7809b2870bd8cc0
[1] d49ab568a2cc5231ac12267a9e74eaf16ca45f9e

0 files changed, 0 insertions, 0 deletions