model-conversion : remove -st targets for converted model (#18689)

model-conversion : remove -st targets for converted model (#18689)

This commit removes the '-st` make target for running the converted
embedding model.

The motivation for this is that the pooling type is now part of the
.gguf metdata of the model and this is used by llama-debug when running
the model. So there is no need to specify the pooling type separately
any more.

The commit also adds an option to specify the type of normalization
applied to the output embeddings when running the converted model.

And the readme documentation has been  updated to reflect these changes.