Track: Revert some needless differences vs upstream in Matcher.java

Android Matcher.start(int) declared "throws IllegalStateException",
which is correct but redundant. Upstream OpenJDK8u121-b13 does not
have this declaration. Another CL in this topic drops the declaration,
without changing behavior.

Bug: 35910877
Test: Treehugger

Change-Id: I59778f13f0df8bd4112af4edc25ee5a93084ae35

api/current.txt

@@ -68706,7 +68706,7 @@ package java.util.regex {
     method public java.util.regex.Matcher reset();
     method public java.util.regex.Matcher reset(java.lang.CharSequence);
     method public int start();
-    method public int start(int) throws java.lang.IllegalStateException;
+    method public int start(int);
     method public int start(java.lang.String);
     method public java.util.regex.MatchResult toMatchResult();
     method public java.util.regex.Matcher useAnchoringBounds(boolean);