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 <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Joyee Cheung <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Refael Ackermann <[email protected]>
Reviewed-By: Sakthipriyan Vairamani <[email protected]>

.travis.yml

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