service/debugger: Rename processMutex to targetMutex
service/debugger: Rename processMutex to targetMutex

Fixes a long standing dangling TODO item.

aarzilli/delve,go-delve/delve,go-delve/delve,derekparker/delve,aarzilli/delve,go-delve/delve,aarzilli/delve,derekparker/delve,aarzilli/delve,derekparker/delve,go-delve/delve,go-delve/delve