Access PRODUCT_ variables directly

This CL simplifies the PRODUCTS.$(INTERNAL_PRODUCT).X accesses of
product variables, and removes unnecessary stripping of them.

Replace: '\$\(PRODUCTS\.\$\(INTERNAL_PRODUCT\)\.([^\)]*)\)' with '$(\1)'
Replace: '\$\(strip\s*\$\(PRODUCT_([^\)]*)\)\)' with '$(PRODUCT_\1)'

A few minor manual tweaks.

Bug: 116769560
Test: presubmit
Change-Id: I70c54f1582e3cc780028535960147d99ebc2e0e1