[BUG]: explicitly parameter unbinding doesn't work for `SIMD`

[soraros]

Bug description

As title.

Steps to reproduce

Consider the following:

alias S = SIMD[DType.float64, _]  # error: index reference type '!lit.declref<@stdlib::@builtin::@dtype::@DType>' does not match parameter type '!lit.declref<@stdlib::@builtin::@int::@Int>'

System information

Mojo 24.1 on Docker, Intel Mac

[helehex]

getting rid the the default value for size fixes it

[soraros]

Works on the latest nightly.