Maurya is the name of the dynasty and its founder. The plural is Mauryas. Mauryan is the adjective. Mauryans is not a proper word.
For comparison: Ptolemy, Ptolemies, Ptolemaic, but not Ptolemaics.
Or Gupta, Guptas, Guptan.
Related: D1708, D1709, D1710, D1711, D1712, and D1713.