travis.yml: (Re-)move the --enable-debug jobs

travis.yml: (Re-)move the --enable-debug jobs

We already have similar jobs in the gitlab-CI ("build-some-softmmu" and
"build-user-plugins"), so let's switch one of them to use --enable-debug
instead of --enable-debug-tcg, then we can simply drop these jobs from
the Travis-CI.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Message-Id: <20210211045455.456371-5-thuth@redhat.com>
Message-Id: <20210211122750.22645-5-alex.bennee@linaro.org>