Drop hide-titlebar plugin

Hi,

The plugin hide-titlebar use gtk_window_set_hide_titlebar_when_maximized, but according to the doc it works only if the titlebar is not a custom one. However Eog use a custom titlebar, which means the plugin doesn't work anymore. Also, Eog has the fullscreen mode so (I think) this plugin is no useful anymore.

P.s : I also think the plugins postr and postasa need to be dropped (The first one no longer maintained and frogr doesn't provide a library. The second one, picasa is gone and libgdata hasn't yet provide support for google photos) but I prefer to know what you think.

Thanks