commit 2dbeebdb accidentally changed
ALTER_COLUMN_OPTION and ALTER_COLUMN_STORAGE_TYPE to be separate flags.
InnoDB and Mroonga are only checking for the latter;
the example storage engine is checking for the former only.

The impact of this bug should be incorrect operation of Mroonga when
the column options GROONGA_TYPE, FLAGS are changed.

InnoDB does not define any column options, only table options,
so the flag ALTER_COLUMN_OPTION should never have been set.

Also, remove the unused flag ALTER_DROP_HISTORICAL.