travis: do not waste time cloning unused submodules

Builds only require:
- dtc
- keycodemapdb
- capstone

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
[AJB: drop wget cache]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

.travis.yml

@@ -66,8 +66,7 @@ git:
 before_install:
   - if [ "$TRAVIS_OS_NAME" == "osx" ]; then brew update ; fi
   - if [ "$TRAVIS_OS_NAME" == "osx" ]; then brew install libffi gettext glib pixman ; fi
-  - wget -O - http://people.linaro.org/~alex.bennee/qemu-submodule-git-seed.tar.xz | tar -xvJ
-  - git submodule update --init --recursive
+  - git submodule update --init --recursive capstone dtc ui/keycodemapdb
 before_script:
   - ./configure ${CONFIG} || { cat config.log && exit 1; }
 script: