shader: remove obsolete layout handling code and fix variable names

Merged Gert Wollny requested to merge gerddie/virglrenderer:fix-array-layout-matching into master

This reinstates 99f8cd3d and removes the suffix from the variable that encodes the array ID.

It can't be assumed that the array IDs are always in the same order for all shaders, but since we removed the use of enhanced layouts, the array id encoding is no longer relevant, because for each SID we can have only one array.

Closes: #266 (closed)

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