android: Drop DisplayPortCalculator.mMainActivity

No need to have a member for this, just pass the
param directly to the VelocityBiasStrategy ctor.

Change-Id: If8fa006afbbb082a0885cef371c89721c64eb3c6
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/194195
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
Tested-by: Jenkins

android/source/src/java/org/mozilla/gecko/gfx/DisplayPortCalculator.java

@@ -21,11 +21,9 @@ final class DisplayPortCalculator {
     private static final int TILE_SIZE = 256;
 
     private DisplayPortStrategy sStrategy;
-    private final LibreOfficeMainActivity mMainActivity;
 
     DisplayPortCalculator(LibreOfficeMainActivity context) {
-        this.mMainActivity = context;
-        sStrategy = new VelocityBiasStrategy(mMainActivity);
+        sStrategy = new VelocityBiasStrategy(context);
     }
 
     DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity) {