Revert "MenuField: Make sure input is a single byte"

This reverts commit 4e075e0f4c60a600a86792d9c36eae513f1cda31.
Revert "Menu: check numBytes == 1 on KeyDown"

This reverts commit 44dc533861d5e6c8c80f3ed89d6dfb4b8a30c724.