Remove unused FCS support for compiling from ASTs

[dsyme]

1. FCS has an ability to take SyntaxTree as inputs instead of text. It was added by @eiriktsarpalis way back, but is to my knowledge entirely unused today - especially given the rate of churn in the specification of SyntaxTree as trivia has been added and other things cleaned up. I propose we remove this for simplicity's sake. At some later point we can take parsed inputs as input but there is no value in it at the moment.

2. FCS also has the ability to create dynamic assemblies using Reflection.Emit, using the ilreflect.fs writer, including .NET Framework collectible assemblies. My proposal is we should also remove this, now that FSI has moved to using ilwrite.fs and ilreflect is now deprecated (and can't do things like emit debug symbols). Removing this would clean up a lot of entry point code.

[7sharp9]

1. Was used by the quotation compiler
2. Was used by the stuff I wrote at xamarin for F# playgrounds as well as Edge.fs

All of these are pretty old now, interesting for talking points and the F# annals but all have lead to other projects now. The quotation compiler might still be used in the Linq optimiser lib that @eiriktsarpalis did too though.

[eiriktsarpalis]

It's used by the QuotationCompiler library, but that being said, I never got the chance to fully port that to .NET Core or more recent FSCS versions.

[T-Gro]

Are both points approved to be removed?
I would assume none of the (older) usages mentioned here are considered to be showstoppers as of today. And reducing the entry points surface would help the FCS codebase.

=> I am happy to proceed on this one if nobody gets hurt in the process

[vzarytovskii]

Are both points approved to be removed?
I would assume none of the (older) usages mentioned here are considered to be showstoppers as of today. And reducing the entry points surface would help the FCS codebase.

=> I am happy to proceed on this one if nobody gets hurt in the process

I think so, it's safe to remove them.