Drop older SymbolicUtils and Symbolics version compat

Only support SymbolicUtils 4 and Symbolics 7.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: claude

Project.toml

@@ -25,8 +25,8 @@ ForwardDiff = "0.10, 1"
 SpecialFunctions = "2"
 Statistics = "<0.0.1, 1"
 SymbolicLimits = "0.2.3"
-SymbolicUtils = "2.1, 3, 4"
-Symbolics = "6, 7"
+SymbolicUtils = "4"
+Symbolics = "7"
 TermInterface = "2"
 julia = "1.9"