drop scalarizing

[isaacsas]

Closes https://github.com/SciML/Catalyst.jl/issues/1051

Not handled yet

• [x] parameters are not being left as arrays/vectors when using the two-argument constructor
• [x] scalarizing in the DSL
• [ ] ~scalarizing in spatial code~ I'm not sufficiently familiar with the spatial code, and tests are passing I think, so I will leave this for @TorkelE to handle when he has time. See https://github.com/SciML/Catalyst.jl/issues/1059

WIth this PR the DSL will still scalarize non-parameters, but I believe this is consistent with MTK now.

[isaacsas]

@TorkelE if tests pass I am happy with this (I'd like to get a new release with this out). Can you let me know if it looks OK to you?

I guess the only other question is if this requires a breaking release? I think it may since we are changing how parameters are handled to drop scalarizing, which will break peoples existing codes unfortunately. If you are OK I'll make this V15 and add a note that removing scalarizing is the only change.