doc: Remove outdated syntax

One of the things we learned this year is that no documentation is
better than bad, misleading or false documentation. The documented
Simfony syntax is from three months ago. I will write a short rustbook
for the new syntax, but this will take time. Until then, people should
read the official rustbook on one hand and compare with the Simfony
example programs on the other hand.

https://doc.rust-lang.org/stable/book/

Also remove links to the removed files.

Author: uncomputable

README.md

@@ -18,8 +18,6 @@ jet_verify(jet_eq_32(b, 7));
 
 Take a look at the [example programs](https://github.com/BlockstreamResearch/simfony/tree/master/example_progs).
 
-Learn about [Simfony's syntax](https://github.com/BlockstreamResearch/simfony/tree/master/doc/syntax.md). There is [experimental syntax](https://github.com/BlockstreamResearch/simfony/blob/master/doc/experimental-syntax.md) that is not supported by master yet.
-
 ## MSRV
 
 This crate should compile with any feature combination on **Rust 1.61.0** or higher.