[roll third_party/pigweed] pw_log: Remove optional from protos

In proto3 all fields are optional by default, with the presence or not
being conveyed by the field having its default, zero, or empty value.

The 'optional' keyword is only required when presence with a default
value is meaningfully different from not present.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/97741

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 3fca2a01cc74b77..48df483dbb69d7e
Roller-URL: https://ci.chromium.org/b/8811713185487272305
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8811713185487272305
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I5464c2be75dbafaccdf5d8c04c2870b534eaddae
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/97785
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 3fca2a0..48df483 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 3fca2a01cc74b771cf78383f161a17e5779d014d
+Subproject commit 48df483dbb69d7ecfbe01e7f94832b855758e412