[roll third_party/pigweed] pw_transfer: Rename TransferHandle -> Handle

Removes the redundant `Transfer` prefix in the name of
`pw::transfer::Client::Handle`. An alias is temporarily kept for
existing users.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/189097

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 7c55f06493264d6..6f4be3a99554bce
Roller-URL: https://ci.chromium.org/b/8757181850101779969
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I51052ddc23644682ada6d854064e5af6d0f57299
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/190233
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 7c55f06..6f4be3a 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 7c55f06493264d60e325d855a0e6b23313331eb0
+Subproject commit 6f4be3a99554bcebce4dc622cac844b2d64436f6