Remove okhttp related proguard rules

Issue: androidx/media#10310
#minor-release
PiperOrigin-RevId: 461889651

extensions/okhttp/proguard-rules.txt

 # Proguard rules specific to the OkHttp extension.
 
 # Options specified by https://github.com/square/okhttp/blob/master/README.md
--dontwarn okhttp3.**
 -dontwarn okio.**
 -dontwarn javax.annotation.**
 -dontwarn org.conscrypt.**
--keepnames class okhttp3.internal.publicsuffix.PublicSuffixDatabase