[flexiglass] Verify that NSSL#mQsExpansionFraction is not accessed

NSSL doesn't need to combine multiple sources to know the shade expansion fraction with flexiglass.

Bug: 296118689
Test: run sysui with, and without flexiglass
Flag: EXEMPT mechanical refactor
Change-Id: I0f7a1220a56a4184b38241ee610591497df1a15b