refactor(material/checkbox): remove xml:space attr from svg checkmark (#24461)

It seems that it was accidentally added in the first version of the component. unneeded attribute xml:space is removed.

Author: davidglezz

src/material/checkbox/checkbox.html

@@ -30,7 +30,6 @@
            focusable="false"
            class="mat-checkbox-checkmark"
            viewBox="0 0 24 24"
-           xml:space="preserve"
            aria-hidden="true">
         <path class="mat-checkbox-checkmark-path"
               fill="none"