Removing 'sagittal' and 'tangential' options for mode command

Make modes currently accepts 'tangential' and 'sagittal' for the select argument:

def make_modes(select=None, maxtem=None):
    """Construct a 2D :class:`numpy.ndarray` of HOM indices.

    Parameters
    ----------
    select : sequence, str, optional; default: None
        Identifier for the mode indices to generate. This can be:

        - An iterable of mode indices, where each element in the iterable
          must unpack to two integer convertible values.
        - A string identifying the type of modes to include, must be
          one of "even", "odd", "tangential" (or "x") or "sagittal" (or "y").

Since the introduction of the plane of incidence option for the beamsplitter, it now longer makes sense to have "tangential" be a synonym for "x", since this depends on the plane of incidence used. This MR removes the "sagittal" and "tangential" options from the function and from the docstring