Pruning a library with ProGuard

Question

I am running into the dex limit problem and I would like to avoid using multi-dex. I noticed that okHttp has a separate internal package for spdy and since my app is not using it, I am trying to remove it.

I added this two lines to the proguard.cfg:

-printusage usage.txt
-assumenosideeffects class com.squareup.okhttp.internal.spdy.*

After building my app, I see in the usage.txt there are several com.squareup.okhttp.internal.spdy classes and methods, but when I run the dexdump script I still get:

    okhttp: 1461
        internal: 978
            http: 233
            huc: 160
            io: 18
            spdy: 373
            tls: 19

Can anyone answer what can be happening? Is there another way of removing a package from a library?