Fix various Clang 7 warnings about unused stuff

Namely:
[-Wunneeded-internal-declaration]
[-Wunused-comparison]
[-Wunused-const-variable]
[-Wunused-function]
[-Wunused-private-fields]

Fixes the following Clang 7 warnings:
```
editor/plugins/script_editor_plugin.cpp:1417:20: warning: function '_find_node_with_script' is not needed and will not be emitted [-Wunneeded-internal-declaration]
editor/scene_tree_dock.cpp:1859:14: warning: function '_find_last_visible' is not needed and will not be emitted [-Wunneeded-internal-declaration]

modules/gdscript/gdscript_parser.cpp:7838:19: warning: equality comparison result unused [-Wunused-comparison]

scene/resources/mesh.cpp:549:35: warning: unused variable '_array_types' [-Wunused-const-variable]
scene/resources/mesh.cpp:563:18: warning: unused variable '_format_translate' [-Wunused-const-variable]

drivers/gles3/rasterizer_scene_gles3.cpp:54:28: warning: unused function 'store_transform2d' [-Wunused-function]

core/io/file_access_network.h:50:6: warning: private field 'ml' is not used [-Wunused-private-field]
core/io/file_access_zip.h:93:14: warning: private field 'archive' is not used [-Wunused-private-field]
core/io/resource_format_binary.h:122:6: warning: private field 'bin_meta_idx' is not used [-Wunused-private-field]
core/message_queue.h:47:9: warning: private field 'mutex' is not used [-Wunused-private-field]
main/tests/test_gui.cpp:63:11: warning: private field 'control' is not used [-Wunused-private-field]
modules/gdscript/gdscript_parser.h:558:7: warning: private field 'completion_static' is not used [-Wunused-private-field]
platform/x11/os_x11.h:148:11: warning: private field 'ip_unix' is not used [-Wunused-private-field]
platform/x11/os_x11.h:180:7: warning: private field 'net_wm_icon' is not used [-Wunused-private-field]
platform/x11/os_x11.h:189:6: warning: private field 'audio_driver_index' is not used [-Wunused-private-field]
platform/x11/os_x11.h:190:15: warning: private field 'capture_idle' is not used [-Wunused-private-field]
servers/physics/body_pair_sw.h:79:6: warning: private field 'cc' is not used [-Wunused-private-field]
servers/visual/visual_server_raster.h:62:7: warning: private field 'draw_extra_frame' is not used [-Wunused-private-field]
```

1 files changed, 3 insertions, 8 deletions

diff --git a/platform/x11/os_x11.h b/platform/x11/os_x11.h
index 47ff257455..bb8411e213 100644
--- a/platform/x11/os_x11.h
+++ b/platform/x11/os_x11.h
@@ -34,17 +34,17 @@
 #include "context_gl_x11.h"
 #include "core/os/input.h"
 #include "crash_handler_x11.h"
-#include "drivers/unix/os_unix.h"
-#include "servers/visual_server.h"
-//#include "servers/visual/visual_server_wrap_mt.h"
 #include "drivers/alsa/audio_driver_alsa.h"
 #include "drivers/alsamidi/alsa_midi.h"
 #include "drivers/pulseaudio/audio_driver_pulseaudio.h"
+#include "drivers/unix/os_unix.h"
 #include "joypad_linux.h"
 #include "main/input_default.h"
 #include "power_x11.h"
 #include "servers/audio_server.h"
 #include "servers/visual/rasterizer.h"
+#include "servers/visual_server.h"
+//#include "servers/visual/visual_server_wrap_mt.h"
 
 #include <X11/Xcursor/Xcursor.h>
 #include <X11/Xlib.h>
@@ -145,7 +145,6 @@ class OS_X11 : public OS_Unix {
 	void handle_key_event(XKeyEvent *p_event, bool p_echo = false);
 	void process_xevents();
 	virtual void delete_main_loop();
-	IP_Unix *ip_unix;
 
 	bool force_quit;
 	bool minimized;
@@ -177,8 +176,6 @@ class OS_X11 : public OS_Unix {
 	AudioDriverPulseAudio driver_pulseaudio;
 #endif
 
-	Atom net_wm_icon;
-
 	PowerX11 *power_manager;
 
 	bool layered_window;
@@ -186,8 +183,6 @@ class OS_X11 : public OS_Unix {
 	CrashHandler crash_handler;
 
 	int video_driver_index;
-	int audio_driver_index;
-	unsigned int capture_idle;
 	bool maximized;
 	//void set_wm_border(bool p_enabled);
 	void set_wm_fullscreen(bool p_enabled);