Remove deprecation on toTex function properties

HISTORY.md

@@ -76,8 +76,6 @@
 - Renamed function `typeof` to `typeOf`, `var` to `variance`,
   and `eval` to `evaluate`. (the old function names are reserved keywords
   which can not be used as a variable name).
-- Deprecated having a `.toTex` property attached to functions.
-  Use a custom toTex handler instead.
 - Deprecated the `Matrix.storage` function. Use `math.matrix` instead to create
   a matrix.
 - Deprecated function `math.expression.parse`, use `math.parse` instead.

src/expression/node/FunctionNode.js

@@ -396,7 +396,7 @@ export const createFunctionNode = /* #__PURE__ */ factory(name, dependencies, ({
       latexConverter = latexFunctions[this.name]
     }
 
-    // for backward compatibility (deprecated in v6)
+    // toTex property on the function itself
     if (math[this.name] &&
       ((typeof math[this.name].toTex === 'function') ||
         (typeof math[this.name].toTex === 'object') ||