Adds stripTrailingFs

This function removes padding 'F' characters in a string (e.g., ICCID).

Bug: 38206971
Test: unit test in another cl
Change-Id: If77604576c5bd26404cdc436f8297191664325a4

telephony/java/com/android/internal/telephony/uicc/IccUtils.java

@@ -836,6 +836,13 @@ public class IccUtils {
         return new String(new char[] {HEX_CHARS[(b & 0xFF) >>> 4], HEX_CHARS[b & 0xF]});
     }
 
+    /**
+     * Strip all the trailing 'F' characters of a string, e.g., an ICCID.
+     */
+    public static String stripTrailingFs(String s) {
+        return s == null ? null : s.replaceAll("(?i)f*$", "");
+    }
+
     /**
      * Converts a character of [0-9a-aA-F] to its hex value in a byte. If the character is not a
      * hex number, 0 will be returned.