Remove `@test_nowarn` from tests

[KristofferC]

Failing the tests because of a single deprecation warning or anything getting emitted to stderr is very strong. This package fails tests, cf https://s3.amazonaws.com/julialang-reports/nanosoldier/pkgeval/by_hash/e8caa27_vs_f23fc0d/StochasticDelayDiffEq.1.7.0-rc2-73a7a8e46fe.log

┌ Warning: dt <= dtmin. Aborting. There is either an error in your model specification or the true solution is unstable.
└ @ SciMLBase ~/.julia/packages/SciMLBase/x3z0g/src/integrator_interface.jl:345
SDDEProblem, solve: Test Failed at /workspace/srcdir/usr/share/julia/stdlib/v1.7/Test/src/Test.jl:806
  Expression: isempty(stderr_content)
   Evaluated: isempty("┌ Warning: dt <= dtmin. Aborting. There is either an error in your model specification or the true solution is unstable.\n└ @ SciMLBase ~/.julia/packages/SciMLBase/x3z0g/src/integrator_interface.jl:345\n")
Stacktrace:
 [1] top-level scope
   @ /opt/julia/share/julia/stdlib/v1.7/Test/src/Test.jl:445
 [2] include(mod::Module, _path::String)
   @ Base ./Base.jl:418
 [3] include(x::String)
   @ Main.##274 ~/.julia/packages/SafeTestsets/A83XK/src/SafeTestsets.jl:23
 [4] macro expansion
   @ ~/.julia/packages/StochasticDelayDiffEq/tnNkg/test/runtests.jl:3 [inlined]
 [5] macro expansion
   @ /opt/julia/share/julia/stdlib/v1.7/Test/src/Test.jl:1282 [inlined]
 [6] top-level scope
   @ ~/.julia/packages/StochasticDelayDiffEq/tnNkg/test/runtests.jl:3

[ChrisRackauckas]

That just failed because of a real error 😅