test: rename test to not use System

System is an exported function.
And now it is used to build ODESystem by default

Author: ven-k

test/initializationsystem.jl

@@ -216,7 +216,7 @@ end
     end
 end
 
-@mtkmodel System begin
+@mtkmodel HydraulicSystem begin
     @components begin
         res₁ = Orifice(p′ = 300e5)
         res₂ = Orifice(p′ = 0)
@@ -234,7 +234,7 @@ end
     end
 end
 
-@mtkbuild sys = System()
+@mtkbuild sys = HydraulicSystem()
 initprob = ModelingToolkit.InitializationProblem(sys, 0.0)
 conditions = getfield.(equations(initprob.f.sys), :rhs)
 

test/split_parameters.jl

@@ -285,7 +285,7 @@ end
         end
     end
 
-    @mtkmodel System begin
+    @mtkmodel ApexSystem begin
         @components begin
             subsys = SubSystem()
         end
@@ -300,7 +300,7 @@ end
         end
     end
 
-    @named sys = System()
+    @named sys = ApexSystem()
     sysref = complete(sys)
     sys2 = complete(sys; split = true, flatten = false)
     ps = Set(full_parameters(sys2))