frontend: remove css variable that was only used once

--size-large-mobile was only used on mobile for the balance amount.

Chagned to closest available value which is --size-header. This is
not exactly the same as 1.4rem (22.4px) however 22.4px is not a
font-size that is used anywhere else. With this change the account
view now has same font-size for header as well as balance.

Author: thisconnect

frontends/web/src/components/balance/balance.module.css

@@ -41,7 +41,7 @@
   }
 
   .balanceTable td {
-    font-size: var(--size-large-mobile);
+    font-size: var(--size-header);
     line-height: 1.5;
   }
 

frontends/web/src/style/variables.css

@@ -49,7 +49,6 @@
 
     /* font sizes */
     --size-large: 2rem;
-    --size-large-mobile: 1.4rem;
     --size-header: 24px;
     --size-subheader: 18px;
     --size-default: 14px;