pandabase: Remove reference to DIRECTORY_DLLS

Nothing defines this under any circumstances.

Also this moves the various component EXPCLs and EXPTPs
within the include guard of the entire header.

panda/src/pandabase/pandasymbols.h

@@ -326,12 +326,6 @@
 #define INLINE_GUI INLINE
 #define INLINE_AUDIO INLINE
 
-#endif
-
-
-#if defined(DIRECTORY_DLLS)
-
-#else
 
 #define EXPCL_PANDA_PGRAPH EXPCL_PANDA
 #define EXPTP_PANDA_PGRAPH EXPTP_PANDA