[Debuginfod] Use StringRef::consume_back (NFC)

Author: kazutakahirata

llvm/lib/Debuginfod/Debuginfod.cpp

@@ -245,8 +245,7 @@ static SmallVector<std::string, 0> getHeaders() {
   uint64_t LineNumber = 0;
   for (StringRef Line : llvm::split((*HeadersFile)->getBuffer(), '\n')) {
     LineNumber++;
-    if (!Line.empty() && Line.back() == '\r')
-      Line = Line.drop_back();
+    Line.consume_back("\r");
     if (!isHeader(Line)) {
       if (!all_of(Line, llvm::isSpace))
         WithColor::warning()