Remove unused resource from Android project

1. Run lint under '/SDK/tools/lint',  save the output to file.
• lint . |grep 'to be unused' > /tmp/unused.txt
2. Remove all unused resouces.
• rm `cat /tmp/unused.txt | gawk -F: '{print $1}' |sed -e 's/  *$//'|grep png`
3. Rebuild the project with 'ant release'.