to delete all files that contains "STRING":
rm -rf $(find . -type f -exec grep -l 'STRING' {} \;)
and to delete all empry directories:
find . -empty -type d -delete
UPDATE
from man grep
:
-L, --files-without-match
Suppress normal output; instead print the name of each input file from which no output would normally have been printed. The scanning will stop on the first match.
-l, --files-with-matches
Suppress normal output; instead print the name of each input file from which output would normally have been printed. The scanning will stop on the first match. (-l is specified by POSIX.)