update almg example. remove outdated ch4 example

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: -0.13 :warning:

Comparison is base (4abb43b) 87.93% compared to head (05d3b7a) 87.80%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #155 +/- ## ========================================== - Coverage 87.93% 87.80% -0.13% ========================================== Files 79 79 Lines 3787 3846 +59 ========================================== + Hits 3330 3377 +47 - Misses 457 469 +12 ``` [see 8 files with indirect coverage changes](https://app.codecov.io/gh/deepmodeling/dpgen2/pull/155/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deepmodeling)

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