Merge pull request #623 from termi-official/do/istree-error

Fix faulty istree deprecation

Author: ChrisRackauckas

src/SymbolicUtils.jl

@@ -19,8 +19,7 @@ using TermInterface
 import TermInterface: iscall, isexpr, issym, symtype, head, children,
                       operation, arguments, metadata, maketerm
 
-const istree = iscall
-Base.@deprecate_binding istree iscall
+Base.@deprecate istree iscall
 export istree, operation, arguments, sorted_arguments, similarterm, iscall
 # Sym, Term,
 # Add, Mul and Pow