Goblin: retire Nym from the public toolchains + drop internal test harnesses

- CI (release.yml/build.yml): remove fetch-nym + AWS_LC_SYS_PREBUILT_NASM;
  the default cargo build --release is Tor/arti only now (nip44 fetch kept).
- Cargo.toml: nym-sdk is optional behind the `nym` feature so the default
  build never pulls it.
- Delete the dead Nym-era probes (xrelay_smoke, connect_timing,
  tunnel_measure) that referenced the removed Nym API and broke `cargo test`.
- Untrack the internal E2E harnesses (e2e.rs, nostr_e2e.rs) via .gitignore;
  gate `mod e2e` behind the `e2e-internal` feature so clones still compile.
- Refresh stale Nym comments in build.rs and the build scripts.

scripts/android.sh

@@ -54,8 +54,8 @@ function build_lib() {
   sed -i -e 's/"cdylib","rlib"]/"rlib"]/g' Cargo.toml
   rm -f Cargo.toml-e
 
-  # The Nym mixnet is linked INTO libgrim.so (nym-sdk is a regular dependency),
-  # so there is no separate sidecar binary to cross-build or bundle into jniLibs.
+  # The Tor transport (embedded arti) is linked INTO libgrim.so, so there is no
+  # separate sidecar binary to cross-build or bundle into jniLibs.
 }
 
 ### Build application