DEPR deprecate pd.to_timedelta('1 M') and pd.to_timedelta('1 Y')

[MarcoGorelli]

We have that pd.to_timedelta(1, unit='M') and pd.to_timedelta(1, unit='Y') are deprecated, and so so should these (xref #34979 (comment) ).

Once deprecated, the note added in #34979 should be removed

[avinashpancham]

take