[builtins] Merge two adjacent if-statements in JSConstructStub

R=bmeurer@chromium.org

Review-Url: https://codereview.chromium.org/2602903005
Cr-Commit-Position: refs/heads/master@{#41999}

src/builtins/x64/builtins-x64.cc

@@ -151,9 +151,7 @@ void Generate_JSConstructStubHelper(MacroAssembler* masm, bool is_api_function,
 
       // Retrieve smi-tagged arguments count from the stack.
       __ SmiToInteger32(rax, Operand(rsp, 0 * kPointerSize));
-    }
 
-    if (create_implicit_receiver) {
       // Push the allocated receiver to the stack. We need two copies
       // because we may have to return the original one and the calling
       // conventions dictate that the called function pops the receiver.