Adjusts syntax tests to read-only array length.

test/libsolidity/syntaxTests/array/length/cannot_be_assigned.sol

@@ -0,0 +1,8 @@
+contract c {
+    uint[] storageArray;
+    function f() public {
+        storageArray.length = 3;
+    }
+}
+// ----
+// TypeError: (72-91): Member "length" is read-only and cannot be used to resize arrays.

test/libsolidity/syntaxTests/array/length/cannot_be_assigned_mapping.sol

@@ -0,0 +1,8 @@
+contract C {
+    mapping(uint => uint[]) map;
+    function f() public {
+        map[0].length = 4;
+    }
+}
+// ----
+// TypeError: (80-93): Member "length" is read-only and cannot be used to resize arrays.

test/libsolidity/syntaxTests/array/length/cannot_be_assigned_struct.sol

@@ -0,0 +1,11 @@
+contract C {
+    struct S {
+        uint[] a;
+    }
+    S s;
+    function f() public {
+        s.a.length = 4;
+    }
+}
+// ----
+// TypeError: (95-105): Member "length" is read-only and cannot be used to resize arrays.