Remove remix_tree related methods

[Boss-1s]

Solves issue #529

Changes

Removed remix_tree and remix_tree_pretty_print

Tests

No tests needed

Maybe we could @deprecate instead, since not everyone knows that they removed the remixtree endpoint

[faretek1]

the remixtree function was added by me a few weeks ago, after the current latest release to pypi. there's no need to use @deprecate

[faretek1]

there's a couple more things to remove

(looks like i can't manage to highlight the lines for the github review system, so i'll put some more funcnames/attrnames here):

These can be removed:

L50-51:

        self.remix_tree_children: Optional[list[Project]] = None
        self.remix_tree_parent: Optional[Project] = None

L863

@property
    def remix_depth(self) -> int:
        """
        Get the 'remix depth' of this project - i.e. the number of layers of remixing until one reaches the remix root.
        """
        if self.remix_tree_children is None:
            self.remix_tree()
        depth = 0
        p = self
        while p.remix_tree_parent:
            # this could also be done recursively, but it can hit the recursion limit in extreme cases
            # > and this happens often, because of remix chains
            p = p.remix_tree_parent
            depth += 1
        return depth

[faretek1]

Thanks, lgtm