RFR: 1741: Change the logic of removing CSR label when CSR label is added via '/csr needed' command

[Zhao Song]

Assuming there is such a situation: 

1. One pr solves issue1 and issue2. 
2. One user thought this pr needs CSR Issue and commented '/csr needed'. 
3. Author of this pr created csr1 of issue1, but then he thought it is not right to create csr of issue1 and withdrawn csr1. 
4. Author of this pr created csr2 of issue2 and csr2 got approved. 
5. In my opinion, the csr label should be removed(But due to [SKARA-1729](https://bugs.openjdk.org/browse/SKARA-1729), it is not removed) 

To sum, 

There are two ways that CSR label can be added to a PR 
1. via '/csr needed' command 
2. A CSR issue is discovered 

For the first case, if the CSR label is added via '/csr needed', there will be a CSR_NEEDED_MARKER. 
In this case, if we want to remove the csr label. there are two ways 
(1) No active CSR Issue exists and use '/csr unneeded' command 
(2) all of the CSR issues are approved or withdrawn(at least 1 CSR Issue is approved) 

For the second case, if the CSR label is added because a CSR Issue is discovered, there will not be CSR_NEEDED_MARKER. 
In this case, if we want to remove the csr label, there is only one way 
(1) all of the CSR issues are approved or withdrawn

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Commit messages:
 - SKARA-1741

Changes: https://git.openjdk.org/skara/pull/1454/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1454&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1741
  Stats: 15 lines in 2 files changed: 2 ins; 3 del; 10 mod
  Patch: https://git.openjdk.org/skara/pull/1454.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1454/head:pull/1454

PR: https://git.openjdk.org/skara/pull/1454