Don't let MBM pass raw_samples to optimize_acqf_discrete

Summary:
pytorch/botorch#2390 broke workflows that were passing this argument, which used to be silently ignored. This is a hotfix that will stop those usages from failing.

More details: Combinerator integ tests failing with:

```
TypeError: optimize_acqf_discrete() got an unexpected keyword argument 'raw_samples'
```

e.g., https://fburl.com/logarithm/kyr18i16 (scuba query: https://fburl.com/scuba/fblearner_workflow_run_status/hid8tp94).

Reviewed By: dme65

Differential Revision: D59161641

fbshipit-source-id: 16aae81c03016e68ed866e29c61e3ffb1d317b95

ax/models/torch/botorch_modular/acquisition.py

@@ -530,6 +530,11 @@ def optimize(
                 )
                 n = num_choices
 
+            # `raw_samples` is not supported by `optimize_acqf_discrete`.
+            # TODO[santorella]: Rather than manually removing it, we should
+            # ensure that it is never passed.
+            if optimizer_options is not None:
+                optimizer_options.pop("raw_samples")
             discrete_opt_options = optimizer_argparse(
                 self.acqf,
                 bounds=bounds,