Don't duplicate OS::ActivationFrameAlignment() for every POSIX platform.

src/platform-linux.cc

Index: src/platform-linux.cc
diff --git a/src/platform-linux.cc b/src/platform-linux.cc
index fb784d1f53d42c61cbaabd10e162b449ade5ec6e..5c252bbf884b9c176644fdbfd47214f96ed516db 100644
--- a/src/platform-linux.cc
+++ b/src/platform-linux.cc
@@ -308,20 +308,6 @@ bool OS::MipsCpuHasFeature(CpuFeature feature) {
 #endif  // def __mips__
 
 
-int OS::ActivationFrameAlignment() {
-#if V8_TARGET_ARCH_ARM
-  // On EABI ARM targets this is required for fp correctness in the
-  // runtime system.
-  return 8;
-#elif V8_TARGET_ARCH_MIPS
-  return 8;
-#endif
-  // With gcc 4.4 the tree vectorization optimizer can generate code
-  // that requires 16 byte alignment such as movdqa on x86.
-  return 16;
-}
-
-
 const char* OS::LocalTimezone(double time) {
   if (std::isnan(time)) return "";
   time_t tv = static_cast<time_t>(floor(time/msPerSecond));