Fix damlc warnings & compile flags (#12404)

`--ghc-option=-Werror` turns warnings into errors, `--ghc-option=-Wwarn`
undoes exactly that so this clearly was not doing anything sensible.

changelog_begin
changelog_end

language-support/java/codegen/src/ledger-tests/daml/Stakeholders.daml

@@ -1,6 +1,6 @@
 -- Copyright (c) 2022 Digital Asset (Switzerland) GmbH and/or its affiliates. All rights reserved.
 -- SPDX-License-Identifier: Apache-2.0
-
+{-# OPTIONS -Wno-controller-can #-}
 
 module Stakeholders where
 

ledger/test-common/src/main/daml/semantic/TimeTests.daml

@@ -3,8 +3,6 @@
 
 module TimeTests where
 
-import DA.Time
-
 template TimeChecker
   with
     party: Party

rules_daml/daml.bzl

@@ -147,7 +147,7 @@ _daml_build = rule(
         ),
         "ghc_options": attr.string_list(
             doc = "Options passed to GHC.",
-            default = ["--ghc-option=-Werror", "--ghc-option=-Wwarn", "--log-level=WARNING"],
+            default = ["--ghc-option=-Werror", "--log-level=WARNING"],
         ),
         "damlc": _damlc,
     },
@@ -256,7 +256,7 @@ _inspect_dar = rule(
 
 _default_project_version = "1.0.0"
 
-default_damlc_opts = ["--ghc-option=-Werror", "--ghc-option=-Wwarn", "--log-level=WARNING"]
+default_damlc_opts = ["--ghc-option=-Werror", "--log-level=WARNING"]
 
 def damlc_for_target(target):
     if not target or target in COMPILER_LF_VERSIONS: