p2p/simulations: remove packages (ethereum#30250)

Looking at the history of these packages over the past several years, there
haven't been any meaningful contributions or usages:
https://github.com/ethereum/go-ethereum/commits/master/p2p/simulations?before=de6d5976794a9ed3b626d4eba57bf7f0806fb970+35

Almost all of the commits are part of larger refactors or low-hanging-fruit contributions.
Seems like it's not providing much value and taking up team + contributor time.

.github/CODEOWNERS

@@ -21,7 +21,4 @@ light/                          @zsfelfoldi @rjl493456442
 node/                           @fjl
 p2p/                            @fjl @zsfelfoldi
 rpc/                            @fjl @holiman
-p2p/simulations                 @fjl
-p2p/protocols                   @fjl
-p2p/testing                     @fjl
 signer/                         @holiman