Fix the usage of pair_coeff in auto_test

[AnguseZhang]

See #567 and #697

[codecov-commenter]

Codecov Report

Merging #698 (ffdce01) into devel (9e3b958) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##            devel     #698   +/-   ##
=======================================
  Coverage   33.94%   33.94%           
=======================================
  Files          86       86           
  Lines       15424    15424           
=======================================
  Hits         5235     5235           
  Misses      10189    10189           

Impacted Files	Coverage Δ
dpgen/auto_test/lib/lammps.py	27.12% <100.00%> (ø)

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[njzjz]

Please also fix

dpgen/dpgen/auto_test/template/elastic/lmp/potential.mod

Line 7 in 9e3b958

pair_coeff

and other related codes.

[AnguseZhang]

pair_coeff

Does a normal LAMMPS without DeePMD also require pair_coeff * *? @njzjz

[njzjz]

pair_coeff

Does a normal LAMMPS without DeePMD also require pair_coeff * *? @njzjz

I think it't not support any more in a new version of LAMMPS.

[wanghan-iapcm]

See also #696