Inline rhs extraction instead of internal Symbolics.rhss

`Symbolics.rhss` is an undocumented one-line internal helper
(`rhss(xs) = map(x->x.rhs, xs)`, not exported). Replace the single use in
deim.jl with the equivalent comprehension and drop its ExplicitImports
non-public allow-list entry, so we don't depend on a Symbolics internal.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ChrisRackauckas

src/deim.jl

@@ -146,7 +146,7 @@ function deim(
     ModelingToolkit.get_var_to_name(sys)[Symbolics.getname(ŷ)] = Symbolics.unwrap(ŷ)
 
     deqs, eqs = get_deqs(sys) # split eqs into differential and non-differential equations
-    rhs = Symbolics.rhss(deqs)
+    rhs = [eq.rhs for eq in deqs]
     # a sparse matrix of coefficients for the linear part,
     # a vector of constant terms and a vector of nonlinear terms about dvs
     A, g, F = separate_terms(rhs, dvs, iv)

test/qa/qa.jl

@@ -30,7 +30,7 @@ run_qa(
                 :get_eqs, :get_initial_conditions, :get_iv, :get_observed,
                 :get_unknowns, :get_var_to_name, :topsort_equations,
                 # not public in Symbolics
-                :getname, :scalarize, :unwrap, :rhss, :value,
+                :getname, :scalarize, :unwrap, :value,
                 # not public in SymbolicUtils
                 :isadd, :ismul,
             ),