build: remove redundant pyenv call in Travis build

PR-URL: https://github.com/nodejs/node/pull/27247


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>