Investigate whether the server can work without client file hacks

[sodic]

Context: #1584 (comment)

Note

It makes sense to tackle this first: #1854

Can we remove the client-specific options in our server/tsconfig.json?

With the current setup, it depends on how typescript (or rollup) chooses which files to process:

• If it's "by demand" (i.e., only process what you need), then we probably don't need the hacks.
• If it's "by includes directories" (i.e., process all files in directories that are part of the project), then we probably need them.

I don't know which one is it, so we should investigate.

[sodic]

I've removed the client hacks. We don't seem to need them anymore: #1862.