Remove stray proguard files

extensions/ima/src/main/proguard-rules.txt

-# Proguard rules specific to the IMA extension.
-
--keep class com.google.ads.interactivemedia.** { *; }
--keep interface com.google.ads.interactivemedia.** { *; }
--keep class com.google.obf.** { *; }
--keep interface com.google.obf.** { *; }

library/dash/src/main/proguard-rules.txt

-# Proguard rules specific to the dash module.
-
-# Constructors accessed via reflection in SegmentDownloadAction
--dontnote com.google.android.exoplayer2.source.dash.offline.DashDownloadAction
--keepclassmembers class com.google.android.exoplayer2.source.dash.offline.DashDownloadAction {
-  static ** DESERIALIZER;
-}

library/hls/src/main/proguard-rules.txt

-# Proguard rules specific to the hls module.
-
-# Constructors accessed via reflection in SegmentDownloadAction
--dontnote com.google.android.exoplayer2.source.hls.offline.HlsDownloadAction
--keepclassmembers class com.google.android.exoplayer2.source.hls.offline.HlsDownloadAction {
-  static ** DESERIALIZER;
-}

library/smoothstreaming/src/main/proguard-rules.txt

-# Proguard rules specific to the smoothstreaming module.
-
-# Constructors accessed via reflection in SegmentDownloadAction
--dontnote com.google.android.exoplayer2.source.smoothstreaming.offline.SsDownloadAction
--keepclassmembers class com.google.android.exoplayer2.source.smoothstreaming.offline.SsDownloadAction {
-  static ** DESERIALIZER;
-}