remove superfluous byte swap in linkersymbol builtin translation (#455)

- Remove the superfluous byte swap in the `linkersymbol` builtin
translation.
- Support testing the `linkersymbol` builtin translation in the runner
specs.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/integration/contracts/Library.sol

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity >=0.6.2;
+
+library L {
+    function f() public returns(uint r) {
+        r = 10;
+    }
+}

crates/integration/contracts/Linked.sol

@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity >=0.6.2;
+
+import "contracts/Library.sol";
+
+/* runner.json
+{
+    "differential": false,
+    "actions": [
+        {
+            "Instantiate": {
+                "origin": "Bob",
+                "code": {
+                    "Solidity": {
+                        "contract": "L",
+                        "path": "contracts/Library.sol"
+                    }
+                }
+            }
+        },
+        {
+            "Instantiate": {
+                "code": {
+                    "Solidity": {
+                        "contract": "Linked",
+                        "path": "contracts/Linked.sol",
+                        "libraries": {
+                            "contracts/Library.sol": {
+                                "L": "0x17bb6d1a8161a52422f86e4460600bdbefc1becd"
+                            }
+                        }
+                    }
+                }
+            }
+        },
+        {
+            "Call": {
+                "dest": {
+                    "Instantiated": 1
+                },
+                "data": "dffeadd0"
+            }
+        },
+        {
+            "VerifyCall": {
+                "success": true,
+                "output": "000000000000000000000000000000000000000000000000000000000000000a"
+            }
+        }
+    ]
+}
+*/
+
+contract Linked {
+    function main() public returns (uint) {
+        return L.f();
+    }
+}