[memory refactor][1/n] Rename Memory -> VectorIO, MemoryBanks -> VectorDBs (#828)

See https://github.com/meta-llama/llama-stack/issues/827 for the broader
design.

This is the first part:

- delete other kinds of memory banks (keyvalue, keyword, graph) for now;
we will introduce a keyvalue store API as part of this design but not
use it in the RAG tool yet.
- renaming of the APIs

llama_stack/providers/remote/vector_io/sample/sample.py

@@ -0,0 +1,22 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+from llama_stack.apis.memory import Memory
+from llama_stack.apis.memory_banks import MemoryBank
+from .config import SampleConfig
+
+
+class SampleMemoryImpl(Memory):
+    def __init__(self, config: SampleConfig):
+        self.config = config
+
+    async def register_memory_bank(self, memory_bank: MemoryBank) -> None:
+        # these are the memory banks the Llama Stack will use to route requests to this provider
+        # perform validation here if necessary
+        pass
+
+    async def initialize(self):
+        pass