chore(agent): cleanup agent's verbosedebug log (#896)

Don't print `Stack depth: ...` messages. Stack depth can be inferred from the
level of indentation used in `nr_php_show_exec` and `nr_php_show_exec_return` -
both use `nr_php_show_exec_indentation`, which uses `NRPRG(php_cur_stack_depth)`
to calculate indentation level.

Author: lavarou

agent/php_execute.c

@@ -2163,9 +2163,6 @@ void nr_php_observer_fcall_begin(zend_execute_data* execute_data) {
   int show_executes = NR_PHP_PROCESS_GLOBALS(special_flags).show_executes;
 
   if (nrunlikely(show_executes)) {
-    nrl_verbosedebug(NRL_AGENT,
-                     "Stack depth: %d after OAPI function beginning via %s",
-                     NRPRG(php_cur_stack_depth), __func__);
     nr_php_show_exec(NR_EXECUTE_ORIG_ARGS);
   }
   nr_php_instrument_func_begin(NR_EXECUTE_ORIG_ARGS);
@@ -2191,9 +2188,6 @@ void nr_php_observer_fcall_end(zend_execute_data* execute_data,
         = NR_PHP_PROCESS_GLOBALS(special_flags).show_execute_returns;
 
     if (nrunlikely(show_executes_return)) {
-      nrl_verbosedebug(NRL_AGENT,
-                       "Stack depth: %d before OAPI function exiting via %s",
-                       NRPRG(php_cur_stack_depth), __func__);
       nr_php_show_exec_return(NR_EXECUTE_ORIG_ARGS TSRMLS_CC);
     }