eiger change causes configure_arm_trigger_and_disarm_detector to fail lint and test.

[Relm-Arrowny]

https://github.com/bluesky/ophyd-async/pull/1152/files is breaking test and it link to this #1745

Acceptance Criteria

• lint and test both passes

[Relm-Arrowny]

bluesky/ophyd-async#1165 fixes the test but lint is failing due to None.

[DominicOram]

As discussed with @jacob720. nexpi is only used in extg mode, see bluesky/ophyd-async#1117 (comment). We're not actually using extg mode anywhere and so we can remove setting it in set_cam_pvs. This probably also means we can remove it in the fastCS Eiger too but it's doing no real harm