libcamera: Remove StreamRoles alias

Now that `Camera::generateConfiguration()` takes a `libcamera::Span`
of `StreamRole`, remove the `StreamRoles` type, which was an alias
to `std::vector<libcamera::StreamRole>`.

The removal has two reasons:
 - it is no longer strictly necessary,
 - its presence may suggest that that is the preferred (or correct)
   way to build/pass a list of `StreamRole`.

Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
[Kieran: Fix small checkstyle report on roles initialiser]
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/stream.h

@@ -69,8 +69,6 @@ enum class StreamRole {
 	Viewfinder,
 };
 
-using StreamRoles = std::vector<StreamRole>;
-
 std::ostream &operator<<(std::ostream &out, StreamRole role);
 
 class Stream