Redesign the way to initialize a graph and revert remove

[siyuan0322]

What do these changes do?

• Use session.g() to initialize the graph instead of Graph().
• Revert the remove syntax.

Related issue number

Related to #134

[codecov-io]

Codecov Report

Merging #199 (2fb567d) into main (4f5db65) will increase coverage by 0.18%.
The diff coverage is 76.92%.

@@            Coverage Diff             @@
##             main     #199      +/-   ##
==========================================
+ Coverage   78.35%   78.54%   +0.18%     
==========================================
  Files          53       53              
  Lines        4986     4941      -45     
==========================================
- Hits         3907     3881      -26     
+ Misses       1079     1060      -19     

Impacted Files	Coverage Δ
python/graphscope/analytical/app/bfs.py	88.88% <ø> (ø)
python/graphscope/analytical/app/cdlp.py	100.00% <ø> (ø)
python/graphscope/analytical/app/clustering.py	83.33% <ø> (ø)
...hon/graphscope/analytical/app/degree_centrality.py	71.42% <ø> (ø)
...raphscope/analytical/app/eigenvector_centrality.py	62.50% <ø> (ø)
python/graphscope/analytical/app/hits.py	55.55% <ø> (ø)
python/graphscope/analytical/app/k_core.py	83.33% <ø> (ø)
python/graphscope/analytical/app/k_shell.py	100.00% <ø> (ø)
...ython/graphscope/analytical/app/katz_centrality.py	45.45% <ø> (ø)
python/graphscope/analytical/app/lpa.py	100.00% <ø> (ø)
... and 17 more

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