Fix up style of StaticString declarations.

At the top level of a file, "const" is the same as "static const",
and reduce the stuttering.

hphp/runtime/base/array/array_data.cpp

@@ -371,8 +371,9 @@ Variant ArrayData::current() const {
   return false;
 }
 
-static const StaticString s_value("value");
-static const StaticString s_key("key");
+const StaticString
+  s_value("value"),
+  s_key("key");
 
 Variant ArrayData::each() {
   if (size_t(m_pos) < size_t(size())) {