remove support for *.rc files

We're now packaging llvm-windres (aosp/1870074) which can be used as a
substitute for GNU binutils' windres, but we've also removed the last
consumer of .rc files in aosp/1867048 (external/mdnsresponder/).

In the worst case, we can bring back support for .rc files but instead
process them with llvm-windres.

Bug: 203794880
Test: lunch aosp_cf_x86_64_phone-userdebug && m
Change-Id: I30a873537e004b46a87191a932d076a89463c873