function isFlatColumn(schemaPath) {
  if (schemaPath.length !== 2) return false
  const [, column] = schemaPath
  if (column.element.repetition_type === 'REPEATED') return false
  if (column.children.length) return false
  return true
}
Returns true if a column is non-nested.

@param {SchemaTree[]} schemaPath
@returns {boolean}