WASM Remove blockhash error (#7121)

* Remove blockhash error

* Update tests.

ethcore/wasm/src/env.rs

@@ -115,7 +115,7 @@ pub const SIGNATURES: &'static [UserFunctionDescriptor] = &[
 	Static(
 		"_blockhash",
 		&[I64, I32],
-		Some(I32),
+		None,
 	),
 	Static(
 		"_coinbase",

ethcore/wasm/src/runtime.rs

@@ -665,7 +665,7 @@ impl<'a, 'b> Runtime<'a, 'b> {
 
 		self.memory.set(return_ptr, &*hash)?;
 
-		Ok(Some(0i32.into()))
+		Ok(None)
 	}
 
 	fn return_address_ptr(&mut self, ptr: u32, val: Address) -> Result<(), InterpreterError>

ethcore/wasm/src/tests.rs

@@ -765,7 +765,7 @@ fn externs() {
 		"Gas limit requested and returned does not match"
 	);
 
-	assert_eq!(gas_left, U256::from(94_733));
+	assert_eq!(gas_left, U256::from(94_858));
 }
 
 #[test]