Unexport yline

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

@@ -4211,7 +4211,7 @@ float entityclass::hplatformat(const int px, const int py)
     return -1000;
 }
 
-int entityclass::yline( int a, int b )
+static int yline( int a, int b )
 {
     if (a < b) return -1;
     return 1;

desktop_version/src/Entity.h

@@ -132,8 +132,6 @@ public:
 
     float hplatformat(int px, int py);
 
-    int yline(int a, int b);
-
     bool entityhlinecollide(int t, int l);
 
     bool entityvlinecollide(int t, int l);