ci: Drop Travis CI

We migrated to gitlab-ci now, and the travis script will only bitrot
over the time.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
12 jobs for next in 31 minutes and 1 second (queued for 24 seconds)
Status Job ID Name Coverage
  Build
passed #181043
arm-4.14-release

00:27:30

passed #181042
arm-4.19-release

00:28:18

passed #181044
arm-4.4-cip-head

00:20:51

passed #181046
arm64-4.14-release

00:27:33

passed #181045
arm64-4.19-release

00:31:00

passed #181053
powerpc-4.19-release

00:15:22

passed #181050
x86-4.14-release

00:19:33

passed #181048
x86-4.19-cip-head

00:20:03

passed #181049
x86-4.19-cip-release

00:20:21

passed #181051
x86-4.4-cip-head

00:16:03

passed #181052
x86-4.4-cip-release

00:17:05

passed #181047
x86-5.4-head

00:21:23