[roll third_party/pigweed] pw_allocator: Remove FreeList and FreeListHeap

These have been replaced by BucketBlocketAllocator, iwhich mplements the
same allocation algorithm by reusing Bucket and BlockAllocator, and thus
satisfies the Allocator API.

The FreeListHeapBuffer class has been retained, and refactored to wrap a
BucketBlockAllocator. Keeping this class facilitates compatibility with
downstream consumers.

Original-Bug: 328076428
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/211914
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https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: c07f0fa93561718..a0b08ffac6e3e91
Roller-URL: https://ci.chromium.org/b/8745232261573365425
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I7fb9acbc3078b6f0437f46a51a42345691947cf5
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/216072
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
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diff --git a/third_party/pigweed b/third_party/pigweed
index c07f0fa..a0b08ff 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit c07f0fa93561718ec4d00ac85bf67137d468d709
+Subproject commit a0b08ffac6e3e9175db299f5a0b8b0aa19fb600b