Move libweston-desktop into libweston

It's not really useful to have libweston without libweston-desktop. It's
also very little code.

Merging both into the same DSO will allow us to cut out a bunch of
indirection and pain.

Signed-off-by: Daniel Stone <daniels@collabora.com>

tests/meson.build

@@ -2,7 +2,7 @@ plugin_test_shell_desktop = shared_library(
 	'weston-test-desktop-shell',
 	'weston-test-desktop-shell.c',
 	include_directories: common_inc,
-	dependencies: [ dep_lib_desktop, dep_libweston_public, dep_libexec_weston, dep_shell_utils ],
+	dependencies: [ dep_libweston_public, dep_libexec_weston, dep_shell_utils ],
 	name_prefix: '',
 	install: false
 )
@@ -241,7 +241,7 @@ tests = [
 		'sources': [
 		  'safe-signal-output-removal-test.c',
 		],
-		'dep_objs': [ dep_lib_desktop, dep_shell_utils ]
+		'dep_objs': [ dep_shell_utils ]
 	},
 ]