Don't define log2 and log2f in blink for Android

The definition of log2f in blink was causing problems on Windows and
is no longer necessary. It is also unnecessary on Android and may
also be causing problems there, so this change finishes removing
the definitions.

See crrev.com/2556383002 for details.

Review-Url: https://codereview.chromium.org/2556383002
Cr-Commit-Position: refs/heads/master@{#437351}
diff --git a/third_party/WebKit/Source/wtf/MathExtras.h b/third_party/WebKit/Source/wtf/MathExtras.h
index 6ff8202..f7da0f3 100644
--- a/third_party/WebKit/Source/wtf/MathExtras.h
+++ b/third_party/WebKit/Source/wtf/MathExtras.h
@@ -59,21 +59,6 @@
 const double twoPiDouble = piDouble * 2.0;
 const float twoPiFloat = piFloat * 2.0f;
 
-#if OS(ANDROID)
-// ANDROID's math.h does not currently supply log2 or log2f.
-inline double log2(double num) {
-  // This constant is roughly M_LN2, which is not provided by default on Windows
-  // and Android.
-  return log(num) / 0.693147180559945309417232121458176568;
-}
-
-inline float log2f(float num) {
-  // This constant is roughly M_LN2, which is not provided by default on Windows
-  // and Android.
-  return logf(num) / 0.693147180559945309417232121458176568f;
-}
-#endif
-
 #if COMPILER(MSVC)
 
 // VS2013 has most of the math functions now, but we still need to work