Remove PNS APIEXPORT that never made sense

It can't work because all base classes must be APIEXPORTed

pcbnew/router/length_tuner_tool.h

@@ -28,7 +28,7 @@
 
 class PNS_TUNE_STATUS_POPUP;
 
-class APIEXPORT LENGTH_TUNER_TOOL : public PNS::TOOL_BASE
+class LENGTH_TUNER_TOOL : public PNS::TOOL_BASE
 {
 public:
     LENGTH_TUNER_TOOL();

pcbnew/router/pns_tool_base.h

@@ -24,7 +24,6 @@
 #define __PNS_TOOL_BASE_H
 
 #include <memory>
-#include <import_export.h>
 
 #include <math/vector2d.h>
 #include <tools/pcb_tool_base.h>
@@ -42,7 +41,7 @@ class PNS_TUNE_STATUS_POPUP;
 namespace PNS
 {
 
-class APIEXPORT TOOL_BASE : public PCB_TOOL_BASE
+class TOOL_BASE : public PCB_TOOL_BASE
 {
 public:
     TOOL_BASE( const std::string& aToolName );

pcbnew/router/pns_walkaround.h

@@ -112,7 +112,7 @@ public:
 
     const RESULT Route( const LINE& aInitialPath );
 
-    void SetLengthLimit( bool aEnable ) 
+    void SetLengthLimit( bool aEnable )
     {
         m_lengthLimitOn = aEnable;
     }

pcbnew/router/router_tool.h

@@ -27,7 +27,7 @@
 
 class PCB_SELECTION_TOOL;
 
-class APIEXPORT ROUTER_TOOL : public PNS::TOOL_BASE
+class ROUTER_TOOL : public PNS::TOOL_BASE
 {
 public:
     ROUTER_TOOL();