Remove unused member function definition in GraphInterface

8 jobs for master
Name Stage Failure
failed
job_clang_py2_amd64 Test There is an unknown failure, please try again
Doctest summary
===============
928 tests
29 failures in tests
0 failures in setup code
1 failure in cleanup code
build finished with problems, 103 warnings.

ERROR: Build failed with: exit status 1
failed
job_gcc_py2_amd64 Test There is an unknown failure, please try again
Doctest summary
===============
928 tests
29 failures in tests
0 failures in setup code
1 failure in cleanup code
build finished with problems, 103 warnings.

ERROR: Build failed with: exit status 1
failed
job_gcc_386 Test There is an unknown failure, please try again
  warnings.warn("tight_layout : falling back to Agg renderer")
/usr/lib/python3/dist-packages/matplotlib/tight_layout.py:225: UserWarning: tight_layout : falling back to Agg renderer
warnings.warn("tight_layout : falling back to Agg renderer")
/usr/lib/python3/dist-packages/matplotlib/tight_layout.py:225: UserWarning: tight_layout : falling back to Agg renderer
warnings.warn("tight_layout : falling back to Agg renderer")
/usr/lib/python3/dist-packages/matplotlib/tight_layout.py:225: UserWarning: tight_layout : falling back to Agg renderer
warnings.warn("tight_layout : falling back to Agg renderer")

ERROR: Build failed with: exit status 1
failed
job_clang_386 Test There is an unknown failure, please try again
168 tests in 1 items.
168 passed and 0 failed.
Test passed.

Document: community
-------------------
builds/c098b1de/1/count0/graph-tool.sh: line 23: 6144 Terminated OMP_NUM_THREADS=1 python3 /usr/bin/sphinx-build -b doctest . build *.rst

ERROR: Build failed with: exit status 143