Follow upstream support for variables (#66)

Because the upstream [PR](https://github.com/nektos/act/pull/1833) already supports variables, so this PR revert #43 (commit de529139af), and cherry-pick commit [6ce45e3](6ce45e3f24).

Co-authored-by: Kuan Yong <wong0514@gmail.com>
Reviewed-on: https://gitea.com/gitea/act/pulls/66
Reviewed-by: Jason Song <i@wolfogre.com>
Co-authored-by: sillyguodong <gedong_1994@163.com>
Co-committed-by: sillyguodong <gedong_1994@163.com>

pkg/jobparser/interpeter.go

@@ -62,8 +62,6 @@ func NewInterpeter(
 		Matrix:   matrix,
 		Needs:    using,
 		Inputs:   nil, // not supported yet
-
-		Vars: nil,
 	}
 
 	config := exprparser.Config{