Use AsciiDoc subscripts instead of latexmath

Author: Pennycook

adoc/chapters/architecture.adoc

@@ -1248,10 +1248,9 @@ single sub-group of size 6.{endnote}
 
 The numbering of work-items in a sub-group reflects the linear numbering of the
 work-items in the work-group.
-Specifically, if a work-item has a linear ID latexmath:[i_s] in the sub-group
-and a linear ID latexmath:[i_w] in the work-group, the work-item with linear ID
-latexmath:[i_s+1] in the sub-group has linear ID latexmath:[i_w+1] in the
-work-group.
+Specifically, if a work-item has a linear ID i~s~ in the sub-group and a linear
+ID i~w~ in the work-group, the work-item with linear ID i~s~+1 in the sub-group
+has linear ID i~w~+1 in the work-group.
 
 Similarly to work-groups, the [code]#group_barrier# function can be used to
 block a work-item until all work-items in the same sub-group arrive at the