Merge VM_PrintJNI and VM_PrintThreads and remove the unused field 'is_deadlock' of DeadlockCycle

Most users use `jstack <pid>` or `kill -3 <pid>` to capture the thread information
This patch merge VM_PrintThreads, VM_PrintJNI, VM_FindDeadlocks into on VM_ExtendedPrintThreads

pros:
1. reduce the overhead of entering and exiting safepoint
2. ensure the consistency of the results of VM_PrintThreads and VM_FindDeadlocks

cons:
1. maximum continuous pause time will increase

After some discussion, We finally decided to merge only VM_PrintJNI and VM_PrintThreads operations. See review comments.