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 <[email protected]>
Signed-off-by: Alex Bennée <[email protected]>
Reviewed-by: Alex Bennée <[email protected]>
Reviewed-by: Wainer dos Santos Moschetta <[email protected]>
Message-Id: <20210211045455[email protected]>
Message-Id: <20210211122750[email protected]>