## What changes were proposed in this pull request?
There are two test data files used for graphx examples existing in directory "graphx/data"
I move it into "data/" directory because the "graphx" directory is used for code files and other test data files (such as mllib, streaming test data) are all in there.
I also update the graphx document where reference the data files which I move place.
## How was this patch tested?
N/A
Author: WeichenXu <WeichenXu123@outlook.com>
Closes#14010 from WeichenXu123/move_graphx_data_dir.
