meson: drop unused argument for i18n.merge_file()

Ignored in Meson < 0.60.0, deprecated since 0.60.1 and fatal since 0.61.0.

data/meson.build:66:2: ERROR: Function does not take positional arguments.
data/meson.build:97:7: ERROR: Function does not take positional arguments.

data/meson.build

@@ -64,7 +64,6 @@ foreach name: desktops
   endif
 
   desktop_target = i18n.merge_file(
-    desktop,
     type: 'desktop',
     input: desktop_in,
     output: desktop,
@@ -95,7 +94,6 @@ foreach session: sessions
   )
 
   i18n.merge_file(
-    session_file,
     type: 'desktop',
     input: desktop_in,
     output: session_file,