Travis switch back to trusty and remove useless repos that may fail the build

.travis.yml

@@ -1,4 +1,4 @@
-dist: bionic
+dist: trusty
 os: linux
 language: minimal
 cache:
@@ -41,6 +41,7 @@ before_install:
 install:
     - if [ -n "$PPA" ]; then travis_retry sudo add-apt-repository "$PPA" -y; fi
     - if [ -n "$DPKG_ADD_ARCH" ]; then sudo dpkg --add-architecture "$DPKG_ADD_ARCH" ; fi
+    - if [ -n "$PACKAGES" ]; then sudo rm -rf /etc/apt/sources.list.d/*; fi
     - if [ -n "$PACKAGES" ]; then travis_retry sudo apt-get update; fi
     - if [ -n "$PACKAGES" ]; then travis_retry sudo apt-get install --no-install-recommends --no-upgrade -qq $PACKAGES; fi
     - if [ "$RUN_TESTS" = "true" ]; then travis_retry sudo apt-get install --no-install-recommends --no-upgrade -qq python3-dev; fi