Remove unneeded flexbug workaround (#40876)

This was only needed for Internet Explorer. Removing it saves a couple of bytes. :-)

REF: https://github.com/philipwalton/flexbugs#flexbug-4

scss/mixins/_grid.scss

@@ -72,7 +72,7 @@
     @include media-breakpoint-up($breakpoint, $breakpoints) {
       // Provide basic `.col-{bp}` classes for equal-width flexbox columns
       .col#{$infix} {
-        flex: 1 0 0%; // Flexbugs #4: https://github.com/philipwalton/flexbugs#flexbug-4
+        flex: 1 0 0;
       }
 
       .row-cols#{$infix}-auto > * {