[FAB-4199] Remove unused variable in core.yaml

There's no usage of the peer.workers config in core.yaml now.

The proposal has been submitted to jira and to the rocketchat channel
for a day to call for comments. No one declares there's any usage.

This patchset removes the variable since there's no further usage.

Change-Id: Id29a2db71a31d41ea5c7c9de9c454734dd4e789d
Signed-off-by: Baohua Yang <yangbaohua@gmail.com>

sampleconfig/core.yaml

@@ -67,7 +67,6 @@ peer:
 
     # Setting for runtime.GOMAXPROCS(n). If n < 1, it does not change the current setting
     gomaxprocs: -1
-    workers: 2
 
     # Gossip related configuration
     gossip: