Remove libwebp old versions that no are failing to compile

As discussed in #12820, these old podspecs (`0.4.0`, `0.3.1`, `0.3.0-rc7`) pointing to tags that no longer compile with the new architecture (`arm64`) need to be removed, so they don't generate confusion. All the features from these older versions are available in the newer versions `0.4.1` or `0.4.2`.