Always set FTZ instead of gating it behind a flag

After a quick round of testing it seems like REAPER doesn't always
enable this on the audio thread, but Bitwig, Ardour, Carla and Renoise
do. So it should be safe to just get rid of the option and to leave this
enabled all the time.

src/plugin/bridges/common.h

@@ -187,9 +187,6 @@ class PluginBridge {
         if (config.editor_xembed) {
             other_options.push_back("editor: XEmbed");
         }
-        if (config.force_ftz) {
-            other_options.push_back("hack: force flush-to-zero");
-        }
         if (config.frame_rate) {
             std::ostringstream option;
             option << "frame rate: " << std::setprecision(2)