TravisCI: Disable clang 3.8 builds (disabled apt repo), remove autotools

.travis.yml

@@ -3,31 +3,17 @@ language: c
 addons:
   apt:
     sources:
-      - llvm-toolchain-precise-3.8
       - ubuntu-toolchain-r-test
     packages:
-      - clang-3.8
       - g++-5
       - gcc-5
 script:
   - ./.travis.sh
 matrix:
   include:
-    - os: linux
-      compiler: gcc
-      env: "BUILD_SYSTEM=autotools"
-    - os: linux
-      compiler: clang
-      env: "BUILD_SYSTEM=autotools"
     - os: linux
       compiler: gcc-5
       env: "BUILD_SYSTEM=cmake"
-    - os: linux
-      compiler: clang-3.8
-      env: "BUILD_SYSTEM=cmake"
     - os: osx
       compiler: clang
       env: "BUILD_SYSTEM=cmake"
-    - os: osx
-      compiler: clang
-      env: "BUILD_SYSTEM=autotools"