BulletRobotics extra lib depends on examples

[skogler]

When building with the CMake option -DBUILD_BULLET2_DEMOS=OFF the linking fails due to the extra lib BulletRoboticsGUI having a dependency on the examples browser library.

[ 96%] Linking CXX shared library libBulletRoboticsGUI.so
/usr/bin/ld: cannot find -lBulletExampleBrowserLib

This should be checked for in the CMake file or the dependency should be resolved/removed.