testutil/environment: remove Execution.OSType field

This field was added in f0e5b3d7d8 to
account for older versions of the engine (Docker EE LTS versions), which
did not yet provide the OSType field in Docker info, and had to be manually
set using the TEST_OSTYPE env-var.

This patch removes the field in favor of the equivalent in DaemonInfo. It's
more verbose, but also less ambiguous what information we're using (i.e.,
the platform the daemon is running on, not the local platform).

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

integration-cli/docker_api_inspect_test.go

@@ -27,7 +27,7 @@ func (s *DockerAPISuite) TestInspectAPIContainerResponse(c *testing.T) {
 
 	var cases []acase
 
-	if testEnv.OSType == "windows" {
+	if testEnv.DaemonInfo.OSType == "windows" {
 		cases = []acase{
 			{"v1.25", append(keysBase, "Mounts")},
 		}