RFR: 8056209 : Remove unused files for libawt

[Phil Race]

https://bugs.openjdk.java.net/browse/JDK-8056209
Proposed removing several files
./windows/native/libawt/sun/java2d/d3d/D3DPipeline.cpp
   ./windows/native/libawt/sun/java2d/d3d/D3DShaderGen.c
   ./windows/native/libawt/sun/windows/WBufferStrategy.cpp

After some analysis the actual list of files to remove is

src/java.desktop/windows/native/libawt/sun/java2d/d3d/D3DPipeline.cpp

- this file appears to be unneeded and has never been built

src/java.desktop/windows/classes/sun/awt/windows\WBufferStrategy.java
src/java.desktop/windows/native/libawt/sun/windows/WBufferStrategy.cpp

- both of these files have not been built since 6u10

D3DShaderGen.c needs to remain. It perhaps should live somewhere else
but it also needs a bit of maintenance. A new bug should be filed on that

here's a webrev for what value it adds :- 
http://cr.openjdk.java.net/~prr/8056209/

I did a full clean windows build to test the change.

-phil.