fix(button): default opacity for disabled clear buttons (ionic-team#18560)

fixes ionic-team#18555

Author: KillerCodeMonkey

core/src/components/button/button.md.scss

@@ -60,7 +60,6 @@
 // --------------------------------------------------
 
 :host(.button-clear) {
-  --opacity: #{$button-md-clear-opacity};
   --background-activated: transparent;
   --background-focused: #{ion-color(primary, base, .1)};
   --background-hover: #{ion-color(primary, base, .04)};
@@ -131,4 +130,4 @@
   :host(.button-outline.ion-color:hover) .button-native {
     background: #{current-color(base, .04)};
   }
-}
+}

core/src/components/button/button.scss

@@ -297,4 +297,4 @@ ion-ripple-effect {
     background: var(--background-hover);
     color: var(--color-hover);
   }
-}
+}