CB-13000: (CI) Speed up android builds

Author: alsorokin

.travis.yml

@@ -25,31 +25,27 @@ matrix:
     android:
       components:
       - tools
-      - tools
   - env: PLATFORM=android-5.1
     os: linux
     language: android
     jdk: oraclejdk8
     android:
       components:
       - tools
-      - tools
   - env: PLATFORM=android-6.0
     os: linux
     language: android
     jdk: oraclejdk8
     android:
       components:
       - tools
-      - tools
   - env: PLATFORM=android-7.0
     os: linux
     language: android
     jdk: oraclejdk8
     android:
       components:
       - tools
-      - tools
 before_install:
 - npm cache clean -f
 - rm -rf ~/.nvm && git clone https://github.com/creationix/nvm.git ~/.nvm && (cd ~/.nvm