Drop electrsd autodownload feature for good

... which requires a bunch of unnecessary dev dependencies, e.g., `zip`.

Instead we lean on the `download_bitcoind_electrs.sh` script also for
local testing.

ci/ci-tests.sh

@@ -25,9 +25,6 @@ PIN_RELEASE_DEPS # pin the release dependencies in our main workspace
 
 export RUST_BACKTRACE=1
 
-# Build `lightning-transaction-sync` in no_download mode.
-export RUSTFLAGS="$RUSTFLAGS --cfg no_download"
-
 echo -e "\n\nBuilding and testing all workspace crates..."
 cargo test --verbose --color always
 cargo check --verbose --color always

lightning-transaction-sync/Cargo.toml

@@ -33,9 +33,4 @@ electrum-client = { version = "0.18.0", optional = true }
 [dev-dependencies]
 lightning = { version = "0.0.123-beta", path = "../lightning", default-features = false, features = ["std", "_test_utils"] }
 tokio = { version = "1.35.0", features = ["full"] }
-
-[target.'cfg(all(not(target_os = "windows"), not(no_download)))'.dev-dependencies]
-electrsd = { version = "0.26.0", default-features = false, features = ["legacy", "esplora_a33e97e1", "bitcoind_25_0"] }
-
-[target.'cfg(all(not(target_os = "windows"), no_download))'.dev-dependencies]
 electrsd = { version = "0.26.0", default-features = false, features = ["legacy"] }