Drop older SciML and JuliaSymbolics major versions from compat

[ChrisRackauckas-Claude]

Please ignore this PR until it has been reviewed by @ChrisRackauckas.

What changed

Pure [compat] edits that drop older major versions of SciML and JuliaSymbolics packages. For each maintained dependency, only the current (non-yanked) major remains; an existing lower bound on that major is kept. No code, tests, or package version were changed.

• lib/CanonicalMoments/Project.toml [deps] Symbolics: 6.29.2, 7.30 → 7.30 (drop 6.29.2; current major is 7)
• lib/OUQBase/Project.toml [deps] SymbolicUtils: 3, 4.38 → 4.38 (drop 3; current major is 4)
• lib/OUQBase/Project.toml [deps] Symbolics: 6.39.1, 7.30 → 7.30 (drop 6.39.1; current major is 7)
• lib/OUQBase/Project.toml [deps] ModelingToolkit: 9.69, 11.31 → 11.31 (drop 9.69; current major is 11)
• lib/OUQBase/Project.toml [deps] SciMLBase: 2.153, 3.31 → 3.31 (drop 2.153; current major is 3)

Why

JuliaSymbolics is treated as part of the SciML-maintained group for this policy. Supporting multiple majors keeps untested resolver windows. Current majors come from JuliaRegistries/General Versions.toml, ignoring yanked = true releases.

Verification

Not verified here: the full test suite, QA, or a live julia-downgrade-compat run.

[ChrisRackauckas-Claude]

Superseded by the corresponding QA work on OptimalUncertaintyQuantification-DEV.jl, per maintainer direction. The DEV branch will carry the SciMLTesting floor and strict QA updates.