[gn build] Port f8cb798

Author: llvmgnsyncbot

llvm/utils/gn/secondary/clang/lib/Driver/BUILD.gn

@@ -94,7 +94,6 @@ static_library("Driver") {
     "ToolChains/PPCFreeBSD.cpp",
     "ToolChains/PPCLinux.cpp",
     "ToolChains/PS4CPU.cpp",
-    "ToolChains/RISCVToolchain.cpp",
     "ToolChains/SPIRV.cpp",
     "ToolChains/SPIRVOpenMP.cpp",
     "ToolChains/SYCL.cpp",