Update used android sdk to 29 version
According to doc: https://docs.aws.amazon.com/lumberyard/latest/userguide/android-setting-up-environment.html
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Also in this file you have setup "NDK_PLATFORM" : "android-21" but in documentation you write to use NDK r20 (the same link and at other pages). As I see WAF base on some Android envirionment variablees as for e.g. ANDROID_SDK_HOME - so it's good to mention about them in documentation (which is step of installing Android SDK, but in some cases is good to know to check it).
Thank for your pull request and all the other GitHub issues you submitted, we will be looking into them!