Remove empty Flotr2 directory

Having this empty directory exist causes `git submodule` commands to
fail with "No submodule mapping found in .gitmodules for path
'dashboard/app/bower_components/Flotr2'".

Signed-off-by: Tim Serong <tserong@suse.com>
Merge pull request #28 from tserong/master

Remove empty Flotr2 directory

Acked-by: Yan-Fa Li <yanfali@gmail.com>