DEV: Skip looking for svgo, gifsicle binaries (PR #12655)

We don’t use these binaries, yet image_optim automatically looks for them when initializing. Skipping avoids some unnecessary work and removes this warning message when running specs:

gifsicle worker: `gifsicle` not found; please provide proper binary or disable this worker (--no-gifsicle argument or `:gifsicle => false` through options)
svgo worker: `svgo` not found; please provide proper binary or disable this worker (--no-svgo argument or `:svgo => false` through options)

See also this PR, it removes svgo binary from the base image.

GitHub