Revert "[gn build] (manually) port 4a16fe13 (debuginfod)"

This reverts commit f0cda715.
4a16fe13 got reverted in f45c9c56.

llvm/utils/gn/secondary/llvm/lib/Debuginfod/BUILD.gn

-static_library("Debuginfod") {
-  output_name = "LLVMDebuginfod"
-  deps = [ "//llvm/lib/Support" ]
-  sources = [ "Debuginfod.cpp" ]
-}

llvm/utils/gn/secondary/llvm/unittests/BUILD.gn

@@ -15,7 +15,6 @@ group("unittests") {
     "DebugInfo/GSYM:DebugInfoGSYMTests",
     "DebugInfo/MSF:DebugInfoMSFTests",
     "DebugInfo/PDB:DebugInfoPDBTests",
-    "Debuginfod:DebuginfodTests",
     "Demangle:DemangleTests",
     "ExecutionEngine:ExecutionEngineTests",
     "ExecutionEngine/JITLink:JITLinkTests",

llvm/utils/gn/secondary/llvm/unittests/Debuginfod/BUILD.gn

-import("//llvm/utils/unittest/unittest.gni")
-
-unittest("DebuginfodTests") {
-  deps = [
-    "//llvm/lib/Debuginfod",
-    "//llvm/lib/Testing/Support",
-  ]
-  sources = [ "DebuginfodTests.cpp" ]
-}