examples/gl_basic: Don't set display name

When calling waffle_display_connect(display_name), gl_basic set
display_name such that it reproduced the same behavior if display_name
were set to NULL. That is, gl_basic wasted code setting display_name to
non-NULL, when the same effect is accomplished by leaving it NULL.

Kill the stupid code. Leave display_name=NULL.

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>