RFR(XXS): 8214001: DependencyContext::remove_dependent_nmethod() deletion in place is unnecessary

[Zhengyu Gu]

Hi,

Please review this small cleanup.

It is not necessary to delete stale entry in place, since it calls 
expunge_stale_entries() to purge all stale entries at the end anyway.


Bug: https://bugs.openjdk.java.net/browse/JDK-8214001
Webrev: http://cr.openjdk.java.net/~zgu/8214001/webrev.00/

Test:

  hotspot_compiler on Linux x64 (fastdebug and release)

Thanks,

-Zhengyu