Merge #176: Remove TOOLCHAIN

43b1bdd Remove TOOLCHAIN (Tobin C. Harding)

Pull request description:

  Cargo already uses an env var `RUSTUP_TOOLCHAIN` that controls the
  toolchain, no need for our custom `TOOLCHAIN` variable.

ACKs for top commit:
  apoelstra:
    ACK 43b1bdd

Tree-SHA512: 6260b3930235df80bf637c227295256a1a187c0d96956c4c6e4adb2777361309e48e4cd092699a30a2bf586cc479eeb841f775b3e7539235c3bd2e11b6f78b44

Author: apoelstra

contrib/test.sh

@@ -6,12 +6,6 @@ if [ "$DO_ALLOC_TESTS" = true ]; then
 	FEATURES="$FEATURES alloc"
 fi
 
-# Use toolchain if explicitly specified
-if [ -n "$TOOLCHAIN" ]
-then
-    alias cargo="cargo +$TOOLCHAIN"
-fi
-
 cargo --version
 rustc --version