Condense intro CSS and remove un-used images (#79120)

client/landing/stepper/declarative-flow/internals/steps-repository/intro/styles.scss

@@ -3,22 +3,16 @@
 @import "../../sensei-variables";
 
 .intro {
-	&.free,
 	&.newsletter {
-		background-color: rgb(162 218 254);
-
 		.step-container {
-			background-image: url(calypso/assets/images/onboarding/newsletter-intro-bottom-mobile.webp);
+			background-color: var(--studio-gray-0);
+			background-image: url(calypso/assets/images/onboarding/newsletter-intro-bottom-neutral.webp);
 			background-repeat: no-repeat;
 			background-attachment: fixed;
 			background-position-x: center;
 			background-position-y: bottom;
 			background-size: contain;
 
-			@include break-medium {
-				background-image: url(calypso/assets/images/onboarding/newsletter-intro-bottom.webp);
-			}
-
 			@media screen and ( max-height: 512px ) and ( orientation: landscape ) {
 				background-size: cover;
 				background-position-y: 35vh;
@@ -29,24 +23,12 @@
 				background-position-y: 10vh;
 			}
 		}
-		.intro__description {
-			max-width: 450px;
-			margin: auto;
-		}
-	}
 
-	&.newsletter {
-		.step-container {
-			background-color: var(--studio-gray-0);
-			background-image: url(calypso/assets/images/onboarding/newsletter-intro-bottom-neutral.webp);
-
-			@include break-medium {
-				background-image: url(calypso/assets/images/onboarding/newsletter-intro-bottom-neutral.webp);
-			}
-		}
 		.intro__description {
 			max-width: 510px;
+			margin: auto;
 		}
+
 		.intro__button::before {
 			content: " ";
 			height: 16px;