🧹 cleaning: Remove Tree#_copy_spine.

Author: make-github-pseudonymous-again

src/3-tree/implementations/0-Empty.js

@@ -76,10 +76,6 @@ Empty.prototype.split = function (_p) {
 	return [this, this];
 };
 
-Empty.prototype._copy_spine = function () {
-	return this;
-};
-
 Empty.prototype._concat_with_deep = function (other) {
 	assert(other instanceof Deep);
 	assert(isSameMeasure(other.M, this.M));

src/3-tree/implementations/1-Single.js

@@ -91,10 +91,6 @@ Single.prototype.split = function (p) {
 	return p(this.measure()) ? [empty(this.M), this] : [this, empty(this.M)];
 };
 
-Single.prototype._copy_spine = function () {
-	return this;
-};
-
 Single.prototype._concat_with_deep = function (other) {
 	assert(other instanceof Deep);
 	assert(isSameMeasure(other.M, this.M));

src/3-tree/implementations/2-Deep.js

@@ -176,10 +176,6 @@ Deep.prototype._concat_with_deep = function (other) {
 	);
 };
 
-Deep.prototype._copy_spine = function () {
-	return new Deep(this.M, this._left, this._middle._copy_spine(), this._right);
-};
-
 Deep.prototype._app3 = function (list, other) {
 	assert(other instanceof Tree);
 	return other._app3_with_deep(list, this);