Restructure vr_ui

Get rid of pixel offset variables, and use makefile variables in
BoardConfigs.

Bug: 37779982
Test: Verified vr ui has same behavior.
Change-Id: Ifbf44e27d7101aedbe3c0e6db4b8181d56efadfd
(cherry picked from commit 81a8e4cab2a20fd1b1a4716563d4d2586bd1e1de)
diff --git a/vr_ui.h b/vr_ui.h
index 85c5708..31ca4a6 100644
--- a/vr_ui.h
+++ b/vr_ui.h
@@ -26,12 +26,10 @@
   protected:
     // Pixel offsets to move drawing functions to visible range.
     // Can vary per device depending on screen size and lens distortion.
-    int x_offset, y_offset, stereo_offset;
+    const int kStereoOffset;
 
     bool InitTextParams() override;
 
-    void DrawHorizontalRule(int* y) override;
-    void DrawHighlightBar(int x, int y, int width, int height) const override;
     void DrawTextLine(int x, int* y, const char* line, bool bold) const override;
 };