Move existing instance removal from init to render

If the instance isn't set to append, other instances on the target element should first be removed/torn down.

I don't foresee any issues with moving this, and all the tests are happy. I'd like to get another set of eyes and cerebral cortices on it, though.

Fixes #1430
I just tried this, and it errors out:

```js
	if ( true ) {
		let foo = 'boo';
		foo += 'boo';
	}
	foo += 'boo';
```

with:
```sh
An error occurred while processing /Users/marty/ractive/.gobble/01-esperanto/1/config/options/data.js (this file was created by the 01-esperanto transformation):
Errors transpiling code: ["line 72: reference to unknown global variable foo"]
------------
```

Yet nothing heinous in transpile (like a closure), if I removed the offending out-of-scope it spits out:

```js
		if ( true ) {
			var foo = 'boo';
			foo += 'boo';
		}
```