Erase needs of job in SingleWorkflow (#9)

Reviewed-on: https://gitea.com/gitea/act/pulls/9
Reviewed-by: Lunny Xiao <[email protected]>
Co-authored-by: Jason Song <[email protected]>
Co-committed-by: Jason Song <[email protected]>

pkg/jobparser/testdata/has_needs.out.yaml

@@ -10,7 +10,6 @@ name: test
 jobs:
   job2:
     name: job2
-    needs: job1
     runs-on: linux
     steps:
       - run: uname -a
@@ -19,7 +18,6 @@ name: test
 jobs:
   job3:
     name: job3
-    needs: [job1, job2]
     runs-on: linux
     steps:
       - run: uname -a