Remove vestiges of m_ConfigDir from Kicad2Step.

The converter uses paths passed in via a config file in the OS's
temp directory.

Fixes https://gitlab.com/kicad/code/kicad/issues/7670

utils/kicad2step/pcb/3d_resolver.cpp

@@ -240,8 +240,7 @@ bool S3D_RESOLVER::createPathList( void )
 
     }
 
-    if( !m_ConfigDir.empty() )
-        readPathList();
+    readPathList();
 
     if( m_Paths.empty() )
         return false;

utils/kicad2step/pcb/3d_resolver.h

@@ -197,7 +197,6 @@ private:
 
     wxString expandVars( const wxString& aPath );
 
-    wxString m_ConfigDir;             ///< 3D configuration directory.
     std::list< SEARCH_PATH > m_Paths; ///< List of base search paths.
 
     ///< Mapping of (short) file names to resolved names.