Remove unused variable.

Originally committed as revision 5757 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -420,7 +420,6 @@ dts="no"
 pp="no"
 mingw32="no"
 mingwce="no"
-cygwin="no"
 os2="no"
 lstatic="yes"
 lshared="no"
@@ -592,7 +591,6 @@ audio_oss="yes"
 dv1394="no"
 vhook="no"
 extralibs=""
-cygwin="yes"
 EXESUF=".exe"
 SLIBPREF="cyg"
 SLIBSUF=".dll"