AP_RPM: remove unneeded initialisations

These should always be static

libraries/AP_RPM/AP_RPM.cpp

@@ -90,14 +90,9 @@ const AP_Param::GroupInfo AP_RPM::var_info[] = {
     AP_GROUPEND
 };
 
-AP_RPM::AP_RPM(void) :
-    num_instances(0)
+AP_RPM::AP_RPM(void)
 {
     AP_Param::setup_object_defaults(this, var_info);
-
-    // init state and drivers
-    memset(state,0,sizeof(state));
-    memset(drivers,0,sizeof(drivers));
 }
 
 /*

libraries/AP_RPM/RPM_PX4_PWM.h

@@ -34,7 +34,7 @@ public:
 private:
     int _fd = -1;
     int _logfd = -1;
-    uint64_t _last_timestamp = 0;
+    uint64_t _last_timestamp;
     uint32_t _resolution_usec = 1;
 
     ModeFilterFloat_Size5 signal_quality_filter {3};