tools: remove unused go_sdk.bzl

This is a leftover from an old attempt at NixOS compatibility.

Change-Id: I5050f76b83f47796cdfa6235db8ee5efe8daf3e2

tools/go_sdk.bzl

@@ -1,31 +0,0 @@
-def _gen_imports_impl(ctx):
-    ctx.file("BUILD", "")
-
-    if "hscloud_root" not in ctx.os.environ:
-        fail("Please souce env.sh")
-
-    is_nixos = "hscloud_nixos" in ctx.os.environ
-    bzl_file_content = """
-load(
-    "@io_bazel_rules_go//go:deps.bzl",
-    "go_register_toolchains",
-    "go_rules_dependencies",
-)
-def load_go_sdk():
-    go_rules_dependencies()
-    go_register_toolchains({go_version})
-    """.format(
-        go_version = 'go_version = "host"' if is_nixos else "",
-    )
-
-    ctx.file("imports.bzl", bzl_file_content)
-
-_gen_imports = repository_rule(
-    implementation = _gen_imports_impl,
-    attrs = dict(),
-)
-
-def gen_imports(name):
-    _gen_imports(
-        name = name,
-    )