Update MTK suggestion to use the stdlib (#422)

* Update MTK suggestion to use the stdlib

* Update symbolics.md

Author: ChrisRackauckas

docs/src/symbolics.md

@@ -41,25 +41,6 @@ ex3 = expand_derivatives(D(D(A(τ))))
 
 ## Using with ModelingToolkit.jl
 
-Most common use case with [ModelingToolkit.jl](https://docs.sciml.ai/ModelingToolkit/stable/) is to plug in interpolation objects as input functions. This can be done using `TimeVaryingFunction` component of [ModelingToolkitStandardLibrary.jl](https://docs.sciml.ai/ModelingToolkitStandardLibrary/stable/).
-
-```@example mtk
-using DataInterpolations
-using ModelingToolkitStandardLibrary.Blocks
-using ModelingToolkit
-using ModelingToolkit: t_nounits as t, D_nounits as D
-using OrdinaryDiffEq
-
-us = [0.0, 1.5, 0.0]
-times = [0.0, 0.5, 1.0]
-A = LinearInterpolation(us, times)
-
-@named src = TimeVaryingFunction(A)
-vars = @variables x(t) out(t)
-eqs = [out ~ src.output.u, D(x) ~ 1 + out]
-@named sys = ODESystem(eqs, t, vars, []; systems = [src])
-
-sys = structural_simplify(sys)
-prob = ODEProblem(sys, [x => 0.0], (times[1], times[end]))
-sol = solve(prob)
-```
+We recommend using the 
+[ModelingToolkitStandardLibrary Interoplation Blocks](https://docs.sciml.ai/ModelingToolkitStandardLibrary/stable/tutorials/input_component/) 
+in order to use DataInterpolations.jl in MTK models.