Remove mdct.o and fft.o from fft-test prerequisites list.

Remove mdct.o and fft.o from fft-test prerequisites list.
Both objects were added to the link command, resulting in multiple definitions
of symbols. Now linking works in the general case when mdct.o and fft.o are
compiled into libavcodec.a.

Originally committed as revision 9097 to svn://svn.ffmpeg.org/ffmpeg/trunk