Removing obsolete NetBeans IDE files from jfx source repo (JDK-8223375)

[Kevin Rushforth]

I propose to remove the obsolete NetBeans IDE files from the JavaFX 
source repo. See JDK-8223375 [1]. Those files were written to run with 
NetBeans 8. We sort of limped along with FX 9 using JDK 8 to browse and 
navigate the sources, but it really doesn't work at all now.

I just downloaded NetBeans 12, which has added support for gradle 6.3, 
to see if I could load and run JavaFX using their gradle plugin (I had 
some mixed success with NetBeans 11.x).

Using JDK 14, and Netbeans' default gradle plugin, I can load the "jfx" 
project, which uses build.gradle to configure the projects> I get no 
warnings or errors now.

The only minor problem I had is that if I close NetBeans with the 
project open, it seems to misplace the subprojects (base, graphics, 
etc.) when I open it back up. I then have to close and reopen the main 
'jfx' project. Then all seems happy again.

If there are no concerns, I will send a out a pull request next week to 
remove the old NB project files.

-- Kevin

[1] https://bugs.openjdk.java.net/browse/JDK-8223375