Remove a file from opus.vcproj

A program source file found its way in here.
Include FLAC on Windows

Yes! This problem had been plaguing me for months. Recently filed issue
#4 and went out looking for help, but then gave it one more try...

Problem turned out to be that the FLAC .vcproj files were linking with
"Multi-threaded" instead of "Multi-threaded DLL" as the rest of my
projects are.
Take out #ifdef GOT_FLAC

No more need for these, thank goodness!