Update SDK Tools to v.24.0.2 and remove wear-20 sys-img

Update SDK Tools version to 24.0.2
Update SDK Tools checksum (sha256sum)
Remove sys-img-armeabi-v7a-android-wear-20 installation by default

Google released a new version of SDK tools, further information here:
https://developer.android.com/sdk/index.html#Other

Download:
http://dl.google.com/android/android-sdk_r24.0.2-linux.tgz

There is a new version sys-img-armeabi-v7a-android-wear-21 and a issue using
docker about available space. This is a quickfix to gain space (1Gb unzipped).
Merge pull request #426 from ardock/pr-update-android-sdk-tools

Update SDK Tools to v.24.0.2 and remove wear-20 sys-img