CUDA refactoring: remove dummy static[int] param in toTensor
Following CUDA branch development, the `static[Backend]` argument in all init proc will be removed. Rationale in [Design Document](https://github.com/mratsim/Arraymancer/blob/aee52ed12bd3028de5172f3709b65f4848a138a8/Design_document.md#have-polymorphic-procs-depending-on-a-backend-parameter).

Due to an upstream bug https://github.com/nim-lang/Nim/issues/6343, an ugly dummy static[int] parameter "dummy_bugfix" has been introduced in [`toTensor`](https://github.com/mratsim/Arraymancer/blob/aee52ed12bd3028de5172f3709b65f4848a138a8/src/arraymancer/init_cpu.nim#L50) proc and [`toTensorReshape`](https://github.com/mratsim/Arraymancer/blob/aee52ed12bd3028de5172f3709b65f4848a138a8/src/arraymancer/term_rewriting.nim#L32) proc.

Hopefully we can remove that ASAP.