Remove Android xr double render (#1297)

This code has been in the Android XR implementation forever, and was
never understood. It did an explicit eglSwapBuffers to present to the
screen, which was needed in Babylon React Native as somehow the bgfx
rendering path was different between the two. Now, even in BRN this
results in double rendering. Maybe this is a result of one of the bgfx
updates. Since it seems to no longer be needed in any scenario, this PR
removes it. Unfortunately XR on Android in the BN Playground is broken
in a different way currently, so I have not been able to verify this
works correctly in that scenario. But previously this code was incorrect
in BN anyway, so I expect this is correct now in both BN and BRN.

Apps/Playground/Android/gradle.properties

@@ -11,3 +11,4 @@ org.gradle.jvmargs=-Xmx1536m
 # This option should only be used with decoupled projects. More details, visit
 # http://www.gradle.org/docs/current/userguide/multi_project_builds.html#sec:decoupled_projects
 # org.gradle.parallel=true
+# jsEngine=JavaScriptCore

BUILDING.md

@@ -213,7 +213,7 @@ used by default if no engine is specified. To change the engine to JavaScriptCor
 the file `Apps\Playground\Android\gradle.properties` and add the following line:
 
 ```
-JSEngine=jsc
+jsEngine=JavaScriptCore
 ```
 
 Once the npm packages are installed, open the project located at

Dependencies/xr/Source/ARCore/XR.cpp

@@ -631,11 +631,6 @@ namespace xr
 
                 // Draw the quad
                 glDrawArrays(GL_TRIANGLE_STRIP, 0, VERTEX_COUNT);
-
-                // Present to the screen
-                // NOTE: For a yet to be determined reason, bgfx is also doing an eglSwapBuffers when running in the regular Android Babylon Native Playground playground app.
-                //       The "double" eglSwapBuffers causes rendering issues, so until we figure out this issue, comment out this line while testing in the regular playground app.
-                eglSwapBuffers(eglGetCurrentDisplay(), eglGetCurrentSurface(EGL_DRAW));
             }
         }