Unexport getgridpoint

It's a method of entityclass even though it doesn't use anything on the
class and it's not used outside of Entity.cpp.

desktop_version/src/Entity.cpp

@@ -14,6 +14,11 @@
 #include "Vlogging.h"
 #include "Xoshiro.h"
 
+static int getgridpoint( int t )
+{
+    return t / 8;
+}
+
 bool entityclass::checktowerspikes(int t)
 {
     if (map.invincibility)
@@ -4094,11 +4099,6 @@ int entityclass::checkactivity(void)
     return -1;
 }
 
-int entityclass::getgridpoint( int t )
-{
-    return t / 8;
-}
-
 bool entityclass::checkplatform(const SDL_Rect& temprect, int* px, int* py)
 {
     //Return true if rectset intersects a moving platform, setups px & py to the platform x & y