libwebp: remove useless variable in gif2webp
libwebp: remove useless variable in gif2webp

"out" is never used.

Change-Id: I4441308ef2267b2a9443add240d2fccabfb817f6

PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,webmproject/libwebp,webmproject/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,PKRoma/libwebp