remove libimagedec from webp_quality, only the webp headers are
inspected. libwebpextras isn't needed by get_disto.
Change-Id: Ib85f97e2c4a9edd97392fd20ef294d1ccc76dda5
This function returns a rough estimation of the quality factor used
for compressing the WebP bitstream.
Simple command line: 'webp_quality [-quiet] in.webp'
should print the estimated quality factor.
Change-Id: Ifba3e489461f5a587003ac9f08cc7556e9b24ac2