remove references to `wa`

pkg/omf/cli/omf_list_installed_packages.fish

 # List all packages installed from the registry.
 function omf_list_installed_packages
   for item in (basename $OMF_PATH/pkg/*)
-    test $item = wa; or echo $item
+    test $item = omf; or echo $item
   end
 end

pkg/omf/cli/omf_list_local_packages.fish

 # List all custom packages and packages installed from the registry.
 function omf_list_local_packages
   for item in (basename {$OMF_PATH,$OMF_CUSTOM}/pkg/*)
-    test $item = wa; or echo $item
+    test $item = omf; or echo $item
   end
 end

pkg/omf/cli/omf_remove_package.fish

 function omf_remove_package
   for pkg in $argv
     if not omf_util_valid_package $pkg
-      if test $pkg = "wa"
-        echo (omf::err)"You can't remove wa"(omf::off) 1^&2
+      if test $pkg = "omf"
+        echo (omf::err)"You can't remove `omf`"(omf::off) 1^&2
       else
         echo (omf::err)"$pkg is not a valid package/theme name"(omf::off) 1^&2
       end