Remove SkImageFilter::Set/GetExternalCache.

These were removed from the .cpp in
be129b26f13d575fd6b396c6ae759838ecc9bd1a, but I forgot to remove them
from the header.

R=bsalomon@google.com, reed@google.com
BUG=skia:

Author: senorblanco@chromium.org

Review URL: https://codereview.chromium.org/492693003
1 file changed