[roll third_party/pigweed] pw_software_update: Clean up TUF and update bundle protos

Clean up the protos used for update bundle and TUF. Flatten the TUF
protos to be more directly the specific types of metadata.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/58880

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 19e41f0f1804226..633d678a5900494
Roller-URL: https://ci.chromium.org/b/8837268680070144097
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8837268680070144097
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I65468d0c1193968fd0dd41ddbae339cbbb9c1729
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/59321
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 19e41f0..633d678 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 19e41f0f180422614e48312b01cc8a70ac409df8
+Subproject commit 633d678a5900494d8ffa7cafee84f818c132815a