删除visualize_graph.py文件，移除不再使用的图形绘制逻辑

src/chat/knowledge/utils/visualize_graph.py

@@ -1,17 +0,0 @@
-import networkx as nx
-from matplotlib import pyplot as plt
-
-
-def draw_graph_and_show(graph):
-    """绘制图并显示，画布大小1280*1280"""
-    fig = plt.figure(1, figsize=(12.8, 12.8), dpi=100)
-    nx.draw_networkx(
-        graph,
-        node_size=100,
-        width=0.5,
-        with_labels=True,
-        labels=nx.get_node_attributes(graph, "content"),
-        font_family="Sarasa Mono SC",
-        font_size=8,
-    )
-    fig.show()