Remove option to create and install contract in the same operation.

This relies on the ability to include multiple Soroban operations in the transaction. We can bring this back if we decide against that.

Stellar-transaction.x

@@ -499,19 +499,6 @@ struct InstallContractCodeArgs
     opaque code<SCVAL_LIMIT>;
 };
 
-enum CreateContractSourceType {
-    CONTRACT_SOURCE_CODE_REF = 0,
-    CONTRACT_SOURCE_INSTALL_CODE = 1
-};
-
-union CreateContractSource switch (CreateContractSourceType type)
-{
-case CONTRACT_SOURCE_CODE_REF:
-    SCContractCode codeRef;
-case CONTRACT_SOURCE_INSTALL_CODE:
-    InstallContractCodeArgs installContractCodeArgs;
-};
-
 union ContractID switch (ContractIDType type)
 {
 case CONTRACT_ID_FROM_SOURCE_ACCOUNT:
@@ -530,7 +517,7 @@ case CONTRACT_ID_FROM_ASSET:
 struct CreateContractArgs
 {
     ContractID contractID;
-    CreateContractSource source;
+    SCContractCode source;
 };
 
 union HostFunction switch (HostFunctionType type)
@@ -664,7 +651,7 @@ case ENVELOPE_TYPE_CREATE_CONTRACT_ARGS:
     struct
     {
         Hash networkID;
-        CreateContractSource source;
+        SCContractCode source;
         uint256 salt;
     } createContractArgs;        
 };