Add missing jni::DeleteLocalRef

[tobrun]

WIP, going over the project to spot missing DeleteLocalRefs.

[jfirebaugh]

This uses jni::PushLocalFrame, so it shouldn't need explicit jni::DeleteLocalRef.

[tobrun]

Thank you for flagging @jfirebaugh, wasn't aware that jni::PushLocalFrame made that possible. Have reverted the changes on the lines in https://github.com/mapbox/mapbox-gl-native/blob/master/platform/android/src/http_file_source.cpp#L88 and will be adding possible other missing delete local refs.