[android] remove manual ref counting on activation/deactivation

platform/android/src/native_map_view.cpp

@@ -120,9 +120,6 @@ gl::ProcAddress NativeMapView::initializeExtension(const char* name) {
 }
 
 void NativeMapView::activate() {
-    if (active++) {
-        return;
-    }
 
     oldDisplay = eglGetCurrentDisplay();
     oldReadSurface = eglGetCurrentSurface(EGL_READ);
@@ -151,10 +148,6 @@ void NativeMapView::activate() {
  * From mbgl::Backend.
  */
 void NativeMapView::deactivate() {
-    if (--active) {
-        return;
-    }
-
     assert(vm != nullptr);
 
     if (oldContext != context && oldContext != EGL_NO_CONTEXT) {

platform/android/src/native_map_view.hpp

@@ -334,8 +334,6 @@ private:
     std::shared_ptr<mbgl::ThreadPool> threadPool;
     std::unique_ptr<mbgl::Map> map;
     mbgl::EdgeInsets insets;
-
-    unsigned active = 0;
 };
 
 } // namespace android