build: remove sudo:false from .travis.yml

sudo:false is being removed by Travis CI. Travis CI recommends removing
the configuration.

Fixes: #24510

PR-URL: #24511
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

.travis.yml

@@ -1,5 +1,4 @@
 language: cpp
-sudo: false
 cache: ccache
 os: linux
 matrix: