Also remove ndk.dir from local.properties since it is getting deprecated
Gradle will only use the info (ndkVersion) in gradle.build. Possibly ndkPath too, but we probably don't need that, since ndk is within the sdk folder (default location)
This does need upgrading at some point and it's basically harmless, but I need
to coordinate upgrading gradle on the buildbot to make it work.
This reverts commit fdf84ed93e.
Updated NDK to r21 (LTS)
Switch target Android to 29 as it is required by Google Play Store
Switch minimum Android to 16 (4.1) as it is the lowest supported version by NDK
Removed MIPS and armeabi as they are no longer supported
Renamed Android build names into official ones