Revert "[Android] Implement mixed resources to fix resource not found"

This reverts commit fbe4a5796cfa27a214a2ef2dc3e7cde3719d9c43.
[Android] Fix resource loading issue of shared mode

Previously, xwalk_runtime_client_shell incorrectly packages
all xwalk resources within it, which hide the resource
loading issue of shared mode.

In commit fbe4a5796, attempting to fix this by creating
MixedResources and override "getResources()" of Context.
But in chromium, there exist bunch of code that get resources
from application context.

In this fix, xwalk will provide an overridden Application
which return XWalkMixedResources for getResources().

In such case, all resource loading within XWalkRuntimeLib will
try first loading from library's Context and then from app's
if not found.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1609
Merge pull request #1907 from wang16/fix_share_file_input

[Android] Fix resource loading issue of shared mode