Remove unused private constants.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=121101188

library/src/main/java/com/google/android/exoplayer/text/eia608/Eia608Parser.java

@@ -91,15 +91,9 @@ public final class Eia608Parser implements
 
   private static final byte CTRL_BACKSPACE = 0x21;
 
-  private static final byte CTRL_MID_ROW_CHAN_1 = 0x11;
-  private static final byte CTRL_MID_ROW_CHAN_2 = 0x19;
-
   private static final byte CTRL_MISC_CHAN_1 = 0x14;
   private static final byte CTRL_MISC_CHAN_2 = 0x1C;
 
-  private static final byte CTRL_TAB_OFFSET_CHAN_1 = 0x17;
-  private static final byte CTRL_TAB_OFFSET_CHAN_2 = 0x1F;
-
   // Basic North American 608 CC char set, mostly ASCII. Indexed by (char-0x20).
   private static final int[] BASIC_CHARACTER_SET = new int[] {
     0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,     //   ! " # $ % & '