refactor BedrockEmbeddings class (#7266)

#### Description
refactor BedrockEmbeddings class to clean code as below:

1. inline content type and accept
2. rewrite input_body as a dictionary literal
3. no need to declare embeddings variable, so remove it

langchain/embeddings/bedrock.py

@@ -107,27 +107,21 @@ class BedrockEmbeddings(BaseModel, Embeddings):
         text = text.replace(os.linesep, " ")
         _model_kwargs = self.model_kwargs or {}
 
-        input_body = {**_model_kwargs}
-        input_body["inputText"] = text
+        input_body = {**_model_kwargs, "inputText": text}
         body = json.dumps(input_body)
-        content_type = "application/json"
-        accepts = "application/json"
 
-        embeddings = []
         try:
             response = self.client.invoke_model(
                 body=body,
                 modelId=self.model_id,
-                accept=accepts,
-                contentType=content_type,
+                accept="application/json",
+                contentType="application/json",
             )
             response_body = json.loads(response.get("body").read())
-            embeddings = response_body.get("embedding")
+            return response_body.get("embedding")
         except Exception as e:
             raise ValueError(f"Error raised by inference endpoint: {e}")
 
-        return embeddings
-
     def embed_documents(
         self, texts: List[str], chunk_size: int = 1
     ) -> List[List[float]]: