STEP import: "Show progress bar when importing" option is clutter

### Problem description

The STEP import dialog has a "Show progress bar when importing" checkbox, which serves no practical purpose for the end user.

### Workbench affected?

None / `Mod/Import`

### Steps to reproduce

Import any STEP file.

### Expected behavior

An import option dialog that's readable and only displays relevant options to the user.

### Actual behavior

Superfluous checkbox exists

This box was introduced with the STEP importer rework back in 2019 with 32ad54c9eff3b47c8f4ef6726fc0a6cfb52034c2, prior to the UX reviews and design groups existing. It neither changes how objects are imported at all, nor is an option an user would want to disable in the first place.

### Development version About Info (in Safe Mode)

```shell
OS: Void Linux (KDE/wayland)
Architecture: x86_64
Version: 26.3.0dev.20260619 (Git shallow) AppImage
Build date: 2026/06/19 20:12:16
Build type: Release
Branch: (HEAD detached at 4109e5de6)
Hash: 4109e5de6baa83b0630a8b999c016d744f165bc8
Python 3.11.14, Qt 6.8.3, Coin 4.0.3, Vtk 9.3.1, boost 1_86, Eigen3 3.4.0, PySide 6.8.3
shiboken 6.8.3, xerces-c 3.3.0, Clipper2 , IfcOpenShell 0.8.2, OCC 7.8.1
Locale: English/United Kingdom (en_GB)
Stylesheet/Theme/QtStyle: FreeCAD.qss/FreeCAD Dark/
Navigation Style/Orbit Style/Rotation Mode: CAD/Rounded Arcball/Drag at cursor
Logical DPI/Physical DPI/Pixel Ratio: 96/92.6073/1
Installed mods:
* Fasteners Workbench 0.5.61
```

### Last known good version (optional)

d26f7720350890bfa467ea8d257ee389f3f9a0f5

Start in the Mod/Import STEP import dialog and reproduce the issue by importing any STEP file. Remove the redundant “Show progress bar when importing” option, then verify that the dialog contains only relevant options and that STEP import still completes normally.

Written by the indexing model from the issue text.