Use default failure message for toBeNaN

It is providing the same functionality by default without a custom error message

spec/core/matchers/toBeNaNSpec.js

@@ -1,11 +1,10 @@
 describe("toBeNaN", function() {
-  it("passes for NaN with a custom .not fail", function() {
+  it("passes for NaN", function() {
     var matcher = j$.matchers.toBeNaN(),
       result;
 
     result = matcher.compare(Number.NaN);
     expect(result.pass).toBe(true);
-    expect(result.message).toEqual("Expected actual not to be NaN.");
   });
 
   it("fails for anything not a NaN", function() {
@@ -27,11 +26,4 @@ describe("toBeNaN", function() {
     result = matcher.compare(Number.POSITIVE_INFINITY);
     expect(result.pass).toBe(false);
   });
-
-  it("has a custom message on failure", function() {
-    var matcher = j$.matchers.toBeNaN(),
-      result = matcher.compare(0);
-
-    expect(result.message).toEqual("Expected 0 to be NaN.");
-  });
 });

src/core/matchers/toBeNaN.js

@@ -7,12 +7,6 @@ getJasmineRequireObj().toBeNaN = function(j$) {
           pass: (actual !== actual)
         };
 
-        if (result.pass) {
-          result.message = "Expected actual not to be NaN.";
-        } else {
-          result.message = "Expected " + j$.pp(actual) + " to be NaN.";
-        }
-
         return result;
       }
     };