processor: Fix memory leak after 88d8114f

This was mistakenly deleted in
https://chromium-review.googlesource.com/c/breakpad/breakpad/+/1155938/12

Change-Id: I95e5d84b36e2f89a7a364ee278ccb128b7d34b50
Reviewed-on: https://chromium-review.googlesource.com/1159525
Reviewed-by: Mark Mentovai <mark@chromium.org>

src/processor/dump_context.cc

@@ -290,6 +290,10 @@ void DumpContext::FreeContext() {
       delete context_.arm;
       break;
 
+    case MD_CONTEXT_ARM64:
+      delete context_.arm64;
+      break;
+
     case MD_CONTEXT_MIPS:
     case MD_CONTEXT_MIPS64:
       delete context_.ctx_mips;