Remove build.nix.sh

This file refers to shell.nix, which was removed in
430e6fed and c00d2f59.

build.nix.sh

-#!/usr/bin/env nix-shell
-#! nix-shell -i bash shell.nix
-
-# This script sets up the build environment by invoking nix-shell shell.nix
-# and then runs the hadrian executable.
-
-function rl {
-    TARGET_FILE="$1"
-
-    cd "$(dirname "$TARGET_FILE")"
-    TARGET_FILE="$(basename "$TARGET_FILE")"
-
-    # Iterate down a (possible) chain of symlinks
-    while [ -L "$TARGET_FILE" ]
-    do
-        TARGET_FILE="$(readlink "$TARGET_FILE")"
-        cd "$(dirname "$TARGET_FILE")"
-        TARGET_FILE="$(basename "$TARGET_FILE")"
-    done
-
-    # Compute the canonicalized name by finding the physical path
-    # for the directory we're in and appending the target file.
-    PHYS_DIR="$(pwd -P)"
-    RESULT="$PHYS_DIR/$TARGET_FILE"
-    echo "$RESULT"
-}
-
-absoluteRoot="$(dirname "$(rl "$0")")"
-echo $absoluteRoot
-cd "$absoluteRoot"
-
-hadrian         \
-  --directory="$absoluteRoot/.." \
-  "$@"