Replace libjpeg-turbo with mozjpeg

[renchap]

According to this PR comments, mozjpeg now performs as well as libjpeg-turbo when not using specific options, and is now the recommended implementation: libvips/libvips#2995

[DarthSim]

Hey @renchap!

mozjpeg with the default param values produces the same result as libjpeg-turbo. Since OSS version of imgproxy does not allow redefining mozjpeg params, replacing libjpeg-turbo with mozjpeg doesn't seem to have any sense.