remove combobox role from dropdown widget

[daniellewhyte]

Summary:

This is causing tons of issues in Safari.

Issue: LIT-1490

Test plan:

[github-actions]

Size Change: -113 B (-0.01%)

Total Size: 1.27 MB

Filename	Size	Change
packages/perseus/dist/es/index.js	415 kB	-113 B (-0.03%)

ℹ️ View Unchanged

Filename	Size
packages/kas/dist/es/index.js	39 kB
packages/keypad-context/dist/es/index.js	760 B
packages/kmath/dist/es/index.js	4.27 kB
packages/math-input/dist/es/index.js	77.9 kB
packages/math-input/dist/es/strings.js	1.79 kB
packages/perseus-core/dist/es/index.js	1.48 kB
packages/perseus-editor/dist/es/index.js	688 kB
packages/perseus-linter/dist/es/index.js	22.2 kB
packages/perseus/dist/es/strings.js	3.7 kB
packages/pure-markdown/dist/es/index.js	3.66 kB
packages/simple-markdown/dist/es/index.js	12.5 kB

_{compressed-size-action}