Use current directory to load prediction model

Before this CL, the testing binary could not execute properly when
invoked directly. This is because the current working directory does not
get set.

To fix this, use the model file from /system/etc when __ANDROID__ is
defined, and refer to the current directory for all other cases.

Test: m libinput_tests && $ANDROID_HOST_OUT/nativetest64/libinput_tests/libinput_tests
Test: atest libinput_tests
Test: atest --host libinput_tests
Bug: 271134652
Change-Id: I0547ca9666eab153208a581fb60f6bef656b946a
diff --git a/include/input/MotionPredictor.h b/include/input/MotionPredictor.h
index fdaffc8..de8ddca 100644
--- a/include/input/MotionPredictor.h
+++ b/include/input/MotionPredictor.h
@@ -67,7 +67,7 @@
      * checkEnableMotionPredition: the function to check whether the prediction should run. Used to
      * provide an additional way of turning prediction on and off. Can be toggled at runtime.
      */
-    MotionPredictor(nsecs_t predictionTimestampOffsetNanos, const char* modelPath = nullptr,
+    MotionPredictor(nsecs_t predictionTimestampOffsetNanos,
                     std::function<bool()> checkEnableMotionPrediction = isMotionPredictionEnabled);
     /**
      * Record the actual motion received by the view. This event will be used for calculating the
@@ -82,7 +82,6 @@
 
 private:
     const nsecs_t mPredictionTimestampOffsetNanos;
-    const std::string mModelPath;
     const std::function<bool()> mCheckMotionPredictionEnabled;
 
     std::unique_ptr<TfLiteMotionPredictorModel> mModel;