scripted-diff: Rename CBufferedFile to BufferedFile

While touching all constructors in the previous commit, the class name
can be adjusted to comply with the style guide.

-BEGIN VERIFY SCRIPT-
 sed -i 's/CBufferedFile/BufferedFile/g' $( git grep -l CBufferedFile )
-END VERIFY SCRIPT-

src/bench/streams_findbyte.cpp

@@ -16,7 +16,7 @@ static void FindByte(benchmark::Bench& bench)
     data[file_size-1] = 1;
     fwrite(&data, sizeof(uint8_t), file_size, file);
     rewind(file);
-    CBufferedFile bf{file, /*nBufSize=*/file_size + 1, /*nRewindIn=*/file_size, 0};
+    BufferedFile bf{file, /*nBufSize=*/file_size + 1, /*nRewindIn=*/file_size, 0};
 
     bench.run([&] {
         bf.SetPos(0);