Revert "TextInputWidget: Update doc'ed requirements for validate function"
Revert "TextInputWidget: Update doc'ed requirements for validate function"

This reverts commit e1eb21a0ba54a0b9916d4b7314d8212508711597.

Change-Id: Id49c0c87b76a2162f6fcdbcc30b0f65bd4d206e3

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui