This WL deprecates using YEAR(4), asking users to use YEAR instead.
The WL also deprecates using UNSIGNED for YEAR. This was un-documented
syntax that had no effect.

The WL also changes SHOW CREATE and INFORMATION_SCHEMA output so
that YEAR is displayed rather than YEAR(4).

The changes apply to tables, views and stored routines and to
SHOW CREATE, DESCRIBE statements and INFORMATION_SCHEMA queries.

Change-Id: I7e28fb15c3a9d379596b79bbd16ede22a6322aa0