Remove unused articles/_splash.html.erb (#17198)

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

app/views/articles/_splash.html.erb

@@ -1,53 +0,0 @@
-<style>
-  .recording-pulse {
-    border: 3px solid #d62d20;
-    -webkit-border-radius: 30px;
-    height: 0.5em;
-    width: 0.5em;
-    display: inline-block;
-    -webkit-animation: pulsate 1s ease-out;
-    -webkit-animation-iteration-count: infinite;
-    opacity: 0.0;
-    margin-right: 10px;
-  }
-
-  @-webkit-keyframes pulsate {
-    0% {
-      -webkit-transform: scale(0.1, 0.1);
-      opacity: 0.0;
-    }
-    50% {
-      opacity: 1.0;
-    }
-    100% {
-      -webkit-transform: scale(1.2, 1.2);
-      opacity: 0.0;
-    }
-  }
-
-  .home-page-splash {
-    padding-top: 8px;
-    padding-bottom: 0px;
-    margin-bottom: -60px;
-    text-align: center;
-    background: #161616;
-    position: relative;
-    z-index: 10;
-  }
-
-  .home-page-splash iframe {
-    width: 100%;
-    height: calc(28vw + 120px);
-    max-height: 500px;
-  }
-
-  @media (max-width: 850px) {
-    .home-page-splash {
-      padding-top: 22px;
-    }
-  }
-</style>
-
-<div class="home-page-splash">
-  <iframe width="560" height="315" src="https://www.youtube.com/embed/f2P_ryNDFdc" frameborder="0" allowfullscreen loading="lazy"></iframe>
-</div>