Fix AoS/SoA stdlib functions to match documentation

(i.e. actually remove the old offset parameter stuff now that
we can actually pass pointers.)

tests_errors/redeclare.ispc

@@ -0,0 +1,6 @@
+// Ignoring redeclaration of symbol "a"
+
+void foo() {
+    int a;
+    int a;
+}

tests_errors/shadow.ispc

@@ -0,0 +1,8 @@
+// Symbol "a" shadows symbol declared in outer scope
+
+void foo() {
+    int a;
+    {
+        int a;
+    }
+}