BigInteger: rm visibility modifiers from static variables

the non static variables don't have privacy modifiers so idk that
the static ones ought to either. phpseclib 3.0 uses privacy
modifiers but not the 2.0 branch

phpseclib/Math/BigInteger.php

@@ -163,23 +163,23 @@ class BigInteger
      *
      * @see __construct()
      */
-    protected static $base;
-    protected static $baseFull;
-    protected static $maxDigit;
-    protected static $msb;
+    static $base;
+    static $baseFull;
+    static $maxDigit;
+    static $msb;
 
     /**
      * $max10 in greatest $max10Len satisfying
      * $max10 = 10**$max10Len <= 2**$base.
      */
-    protected static $max10;
+    static $max10;
 
     /**
      * $max10Len in greatest $max10Len satisfying
      * $max10 = 10**$max10Len <= 2**$base.
      */
-    protected static $max10Len;
-    protected static $maxDigit2;
+    static $max10Len;
+    static $maxDigit2;
     /**#@-*/
 
     /**