renderscript: go from deprecation to removal

(http://b/206676167 is the internal bug for the overall "remove renderscript", http://b/255624710 the more specific "remove *.rscript files from the tree".)

renderscript's been deprecated for a while, but there was no real motivation (and some downside) to actually remove it until now. with risc-v, we either have to (a) backport risc-v support to a decade-old fork of llvm, (b) forward port renderscript to current llvm, or (c) finally remove renderscript. despite the unfortunate disruption to legacy code, option (c) is the least difficult of these choices.

i've removed all the renderscript from frameworks/av/ already (after proving it was unused), and obviously all the renderscript tools and the CTS tests _of renderscript itself_ are easy to delete, but we'll need to manage the Studio side of things (they ship some of the tools).

the main issues are these camera tests, all of which will need to be rewritten:

https://cs.android.com/search?q=f:%5C.rscript$%20-f:cts%2Ftests%2Ftests%2Frenderscript%20-f:cts%2Ftests%2Ftests%2Frscpp%20-f:rsblas%20-f:frameworks%2Fcompile%20-f:frameworks%2Frs%20-f:development%2Fsamples&sq=package:%5Eandroid-internal$