[univalue] Remove autotools

Summary: Now that we no longer follow the (legacy, now archived) upstream there is no reason to keep the autotools files that we don't around.

Test Plan:

ninja all check-univalue

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D16307