Remove HOOK_SVC_START, caused more problems than it was worth

An operator wanting to monitor processes started by Finit could use the
kernel ftrace framework.  E.g. execsnoop in perf-tools.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

docs/plugins.md

@@ -110,11 +110,6 @@ Hooks
 
   **NOTE:** This hook callback gets the lost PID as argument.
 
-* `HOOK_SVC_START`: Like `HOOK_SVC_LOST`, but called when a process is
-  started.  Same caveats apply.
-
-  **NOTE:** This hook callback gets the new PID as argument.
-
 * `HOOK_RUNLEVEL_CHANGE`: Called when the user has issued a runlevel
   change.  The hook is called when services not matching the new
   runlevel have been been stopped.  When the hook has completed, Finit