Revert "Disable L8 Shrinking for release"

This reverts commit b7ccd79f58c64c510627e95a0eefa690c55f7066.

Reason for revert: It works.

Change-Id: I62577b1e5096df5753f86c4320037869757416c2
diff --git a/src/main/java/com/android/tools/r8/L8Command.java b/src/main/java/com/android/tools/r8/L8Command.java
index 646a96a..d96a5a1 100644
--- a/src/main/java/com/android/tools/r8/L8Command.java
+++ b/src/main/java/com/android/tools/r8/L8Command.java
@@ -163,8 +163,8 @@
     }
 
     public boolean isShrinking() {
-       // Disable for release.
-       return false;
+      // Answers true if keep rules, even empty, are provided.
+      return !proguardConfigStrings.isEmpty() || !proguardConfigFiles.isEmpty();
     }
 
     @Override