Apps+Demos+Dialogs: Remove unnecessary minimum window sizes

The new layout system conveniently calculates these for us now.
In the case of Mandelbrot where it needs to be overriden, make
sure to disable obey min widget size first. In EmojiInputDialog's
case, the window needs to be resized instead to center correctly.

Userland/Applications/Calendar/main.cpp

@@ -35,7 +35,6 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     auto window = TRY(GUI::Window::try_create());
     window->set_title("Calendar");
     window->resize(600, 480);
-    window->set_minimum_size(171, 141);
     window->set_icon(app_icon.bitmap_for_size(16));
 
     auto main_widget = TRY(window->try_set_main_widget<GUI::Widget>());

Userland/Applications/SoundPlayer/SoundPlayerWidgetAdvancedView.cpp

@@ -29,7 +29,6 @@ SoundPlayerWidgetAdvancedView::SoundPlayerWidgetAdvancedView(GUI::Window& window
     , m_window(window)
 {
     window.resize(455, 350);
-    window.set_minimum_size(600, 130);
     window.set_resizable(true);
     set_fill_with_background_color(true);
 

Userland/Applications/Welcome/main.cpp

@@ -30,9 +30,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     auto window = TRY(GUI::Window::try_create());
     window->resize(480, 250);
     window->center_on_screen();
-
     window->set_title("Welcome");
-    window->set_minimum_size(480, 250);
     window->set_icon(app_icon.bitmap_for_size(16));
     auto welcome_widget = TRY(window->try_set_main_widget<WelcomeWidget>());
 

Userland/Demos/Mandelbrot/Mandelbrot.cpp

@@ -409,6 +409,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     auto window = TRY(GUI::Window::try_create());
     window->set_double_buffering_enabled(false);
     window->set_title("Mandelbrot");
+    window->set_obey_widget_min_size(false);
     window->set_minimum_size(320, 240);
     window->resize(window->minimum_size() * 2);
     auto mandelbrot = TRY(window->try_set_main_widget<Mandelbrot>());

Userland/Libraries/LibGUI/EmojiInputDialog.cpp

@@ -62,7 +62,7 @@ EmojiInputDialog::EmojiInputDialog(Window* parent_window)
     int dialog_width = button_size * columns + magic_offset;
     int dialog_height = button_size * rows;
 
-    set_minimum_size(dialog_width, dialog_height);
+    resize(dialog_width, dialog_height);
     set_frameless(true);
 
     for (size_t row = 0; row < rows && index < code_points.size(); ++row) {