libpod/container_internal: Make all errors loading explicitly configured hook dirs fatal

Remove this IsNotExist out which was added along with the rest of this
block in f6a2b6bf2b (hooks: Add pre-create hooks for runtime-config
manipulation, 2018-11-19, #1830).  Besides the obvious "hook directory
does not exist", it was swallowing the less-obvious "hook command does
not exist".  And either way, folks are likely going to want non-zero
podman exits when we fail to load a hook directory they explicitly
pointed us towards.

Signed-off-by: W. Trevor King <wking@tremily.us>

libpod/container_internal.go

@@ -1407,10 +1407,6 @@ func (c *Container) setupOCIHooks(ctx context.Context, config *spec.Spec) (exten
 	} else {
 		manager, err := hooks.New(ctx, c.runtime.config.HooksDir, []string{"precreate", "poststop"})
 		if err != nil {
-			if os.IsNotExist(err) {
-				logrus.Warnf("Requested OCI hooks directory %q does not exist", c.runtime.config.HooksDir)
-				return nil, nil
-			}
 			return nil, err
 		}