Don't assume that correctable words are invalid

Currently, the Delight3DictionaryFacilitator sets a boolean flag when the top
suggestion score exceeds the auto-correction threshold. This flag is used to
trigger auto-correction of the typed word. Also, the existing logic assumes
that if allowsToBeAutoCorrected then the word is invalid, which is no longer
true after we stopped using whitelists.

Bug 19518376.

Change-Id: Ifa7f6a09c07d25ac68c6cf3aec91f358bd88689f