[category.ctype] Replace unnecessary placeholder type by the usual 'see below'

Author: tkoeppe

source/locales.tex

@@ -1095,21 +1095,21 @@
 namespace std {
   class ctype_base {
   public:
-    using mask = @\placeholder{T}@;
+    using mask = @\seebelow@;
 
     // numeric values are for exposition only.
-    static const mask space = 1 << 0;
-    static const mask print = 1 << 1;
-    static const mask cntrl = 1 << 2;
-    static const mask upper = 1 << 3;
-    static const mask lower = 1 << 4;
-    static const mask alpha = 1 << 5;
-    static const mask digit = 1 << 6;
-    static const mask punct = 1 << 7;
+    static const mask space  = 1 << 0;
+    static const mask print  = 1 << 1;
+    static const mask cntrl  = 1 << 2;
+    static const mask upper  = 1 << 3;
+    static const mask lower  = 1 << 4;
+    static const mask alpha  = 1 << 5;
+    static const mask digit  = 1 << 6;
+    static const mask punct  = 1 << 7;
     static const mask xdigit = 1 << 8;
-    static const mask blank = 1 << 9;
-    static const mask alnum = alpha | digit;
-    static const mask graph = alnum | punct;
+    static const mask blank  = 1 << 9;
+    static const mask alnum  = alpha | digit;
+    static const mask graph  = alnum | punct;
   };
 }
 \end{codeblock}