Remove "turn device screen on" feature

Only keep "turn device screen off" and POWER button.

After we turn the device screen off (with Ctrl+o), turning it back on
does not always work, and leaves the device in a weird state, where even
the power button may not be sufficient:
<https://github.com/Genymobile/scrcpy/issues/175#issuecomment-497946596>

This is not an acceptable behavior, so disable the shortcut to turn the
physical device screen on. We can use the POWER button (or Ctrl+p)
instead.

README.md

@@ -286,7 +286,6 @@ you are interested, see [issue 14].
  | click on `POWER`                       | `Ctrl`+`p`                    |
  | power on                               | _Right-click²_                |
  | turn device screen off (keep mirroring)| `Ctrl`+`o`                    |
- | turn device screen on                  | `Ctrl`+`Shift`+`o`            |
  | expand notification panel              | `Ctrl`+`n`                    |
  | collapse notification panel            | `Ctrl`+`Shift`+`n`            |
  | copy device clipboard to computer      | `Ctrl`+`c`                    |

app/src/input_manager.c

@@ -282,11 +282,8 @@ input_manager_process_key(struct input_manager *input_manager,
                 }
                 return;
             case SDLK_o:
-                if (control && ctrl && !meta && down) {
-                    enum screen_power_mode mode = shift
-                                                ? SCREEN_POWER_MODE_NORMAL
-                                                : SCREEN_POWER_MODE_OFF;
-                    set_screen_power_mode(controller, mode);
+                if (control && ctrl && !shift && !meta && down) {
+                    set_screen_power_mode(controller, SCREEN_POWER_MODE_OFF);
                 }
                 return;
             case SDLK_DOWN:

app/src/main.c

@@ -134,9 +134,6 @@ static void usage(const char *arg0) {
         "    Ctrl+o\n"
         "        turn device screen off (keep mirroring)\n"
         "\n"
-        "    Ctrl+Shift+o\n"
-        "        turn device screen on\n"
-        "\n"
         "    Ctrl+n\n"
         "       expand notification panel\n"
         "\n"