MTK cannot identify independent variables with new Symbolics convention

[doppioandante]

This works:

@variables t x[1](t)
Dt = Differential(t)
@named sys = ODESystem([Dt(x[1]) ~ 3])

This doesn't:

@variables t x(t)[1]
Dt = Differential(t)
@named sys = ODESystem([Dt(x[1]) ~ 3])

with the following error:

ArgumentError: Variable (x(t))[1] is not a function of independent variable SymbolicUtils.Term{Real, Nothing}[(x(t))[1]].

[YingboMa]

@shashi could you take a look?

[ChrisRackauckas]

Removed the bad constructor