Revert "[android] Do not create Timers on Default main loops"

This reverts commit 13cd75f099.

platform/android/src/timer.cpp

@@ -3,7 +3,6 @@
 #include <mbgl/util/run_loop.hpp>
 #include <mbgl/util/timer.hpp>
 
-#include <cassert>
 #include <functional>
 
 namespace mbgl {
@@ -12,7 +11,6 @@ namespace util {
 class Timer::Impl : public RunLoop::Impl::Runnable {
 public:
     Impl() {
-        assert(!loop->isDefaultLoop);
         loop->initRunnable(this);
     }