crfs: delete

The CRFS project has long since moved, and no one is looking
for it in x/build by now. Remove its directory.

For golang/go#51867.

Change-Id: I91a6b6614d284fbf731d71641870ae2dcb55c67c
Reviewed-on: https://go-review.googlesource.com/c/build/+/394516
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/crfs/README.md b/crfs/README.md
deleted file mode 100644
index fc9c458..0000000
--- a/crfs/README.md
+++ /dev/null
@@ -1,7 +0,0 @@
-# CRFS: Container Registry Filesystem
-
-## Moved
-
-This project has moved to https://github.com/google/crfs.
-
-It's more widely applicable than just for use by Go's build system.