Clean up all scriptclass externs into one location

I have the feeling that none of the devs understood what extern did, and
they kind of just sprinkled it everywhere until things started working.
But like all other classes, it should just be one line in the class's
respective header file, and shouldn't be so messy.

desktop_version/src/Input.cpp

@@ -7,8 +7,6 @@
 
 #include "FileSystemUtils.h"
 
-extern scriptclass script;
-
 void updatebuttonmappings(int bind)
 {
     for (

desktop_version/src/Logic.cpp

@@ -2,8 +2,6 @@
 #include "Script.h"
 #include "Network.h"
 
-extern scriptclass script;
-
 void titlelogic()
 {
     //Misc

desktop_version/src/Render.cpp

@@ -10,8 +10,6 @@
 
 #include "MakeAndPlay.h"
 
-extern scriptclass script;
-
 int tr;
 int tg;
 int tb;

desktop_version/src/Script.h

@@ -64,4 +64,6 @@ public:
      std::vector <std::string>  customscript;
 };
 
+extern scriptclass script;
+
 #endif /* SCRIPT_H */

desktop_version/src/Scripts.cpp

@@ -5,8 +5,6 @@
 
 #include <algorithm>
 
-extern scriptclass script;
-
 void scriptclass::load(std::string t)
 {
     //loads script name t into the array

desktop_version/src/editor.cpp

@@ -2072,8 +2072,6 @@ void fillboxabs( int x, int y, int x2, int y2, int c )
 
 extern editorclass ed;
 
-extern scriptclass script;
-
 void editorclass::generatecustomminimap()
 {
     map.customwidth=mapwidth;

desktop_version/src/editor.h

@@ -46,7 +46,6 @@ struct LevelMetaData
 
 
 extern std::vector<edentities> edentity;
-extern scriptclass script;
 
 class EditorData
 {