pw_kvs: EntryCache tests

- Expand the EntryCache tests.
- Remove unused kWorkingBufferSize variable
- Remove EntryMetadata::deleted() since it isn't widely used and
  overlaps with EntryMetadata::state().

Change-Id: Ic18622acf5ce8f3b303fe9ddd15659163dc2ef55
diff --git a/pw_kvs/BUILD b/pw_kvs/BUILD
index 9700013..76bef4f 100644
--- a/pw_kvs/BUILD
+++ b/pw_kvs/BUILD
@@ -122,7 +122,10 @@
 pw_cc_test(
     name = "entry_cache_test",
     srcs = ["entry_cache_test.cc"],
-    deps = [":pw_kvs"],
+    deps = [
+        ":pw_kvs",
+        ":test_utils",
+    ],
 )
 
 pw_cc_test(