revert: feat(core): Hide header in PWA

Signed-off-by: Simon L. <szaimen@e.mail.de>

core/css/header.scss

@@ -239,18 +239,3 @@
 		}
 	}
 }
-
-@media (display-mode: standalone) or (display-mode: minimal-ui) {
-	#header:not(.header-guest) {
-		display: none !important;
-	}
-
-	#content, #content-vue {
-		margin-top: var(--body-container-margin) !important;
-	}
-
-	:root {
-		// Override the body height to make up for the additional height due to the missing header.
-		--body-height: calc(100% - env(safe-area-inset-bottom) - var(--body-container-margin) * 2) !important;
-	}
-}