[Android] Fix the timer resuming issue

Removing the flag indicating if the timer is paused since the renderer
resources are not destroyed when the activity is destroyed, it is
somewhat by design, and the java side flag will cause inconsistent
state with native side renderer side.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1653
Merge pull request #1918 from hmin/pauseTimers

[Android] Fix the timer resuming issue