Remove arraysize.h gcc hack and Chromium override.

Part of work removing dependency on Chromium's base.

BUG=468375 (in particular comment #37)

Review URL: https://codereview.webrtc.org/1327023002

Cr-Commit-Position: refs/heads/master@{#9880}

webrtc/base/arraysize.h

@@ -24,16 +24,7 @@
 // This template function declaration is used in defining arraysize.
 // Note that the function doesn't need an implementation, as we only
 // use its type.
-template <typename T, size_t N>
-char (&ArraySizeHelper(T (&array)[N]))[N];
-
-// That gcc wants both of these prototypes seems mysterious. VC, for
-// its part, can't decide which to use (another mystery). Matching of
-// template overloads: the final frontier.
-#ifndef _MSC_VER
-template <typename T, size_t N>
-char (&ArraySizeHelper(const T (&array)[N]))[N];
-#endif
+template <typename T, size_t N> char (&ArraySizeHelper(T (&array)[N]))[N];
 
 #define arraysize(array) (sizeof(ArraySizeHelper(array)))