Bluesky plan entry points shouldn't use parameter components

From a discussion between @DominicOram and myself today:

We think it's pointlessly messy to try and construct parameters for each plan entry point from our common components. Instead, each entry point should just define its own base model.

The parameter components can still be used to construct our internal parameters, eg `GridCommon`. These are used by our common experiments, so they really are common parameters.

mx-bluesky should handle conversions between these entry point external parameters and internal parameters. See https://github.com/DiamondLightSource/mx-bluesky/pull/1343 for an example of where this has been done