refactor: SymbolicLinearInterface is only MTK API

Author: AayushSabharwal

src/SciMLBase.jl

@@ -868,7 +868,7 @@ export Clocks, TimeDomain, is_discrete_time_domain, isclock, issolverstepclock,
 
 export ODEAliasSpecifier, LinearAliasSpecifier
 
-@public SymbolicLinearInterface, get_new_A_b, create_parameter_timeseries_collection,
+@public get_new_A_b, create_parameter_timeseries_collection,
         get_saveable_values, save_discretes!
 
 end

src/problems/linear_problems.jl

@@ -1,7 +1,8 @@
 """
     $(TYPEDEF)
 
-A utility struct stored inside `LinearProblem` to enable a symbolic interface.
+A utility struct stored inside `LinearProblem` to enable a symbolic interface. Intended
+for use by ModelingToolkit.jl.
 
 # Fields