[libc++] Remove outdated FIXME comment in ctype<char> (#160008)

The FIXME comment about not hardcoding table_size is unclear about its
original intent.

Author: iidmsa

libcxx/include/__cxx03/__locale

@@ -578,7 +578,7 @@ public:
 #ifdef _CACHED_RUNES
   static const size_t table_size = _CACHED_RUNES;
 #else
-  static const size_t table_size = 256; // FIXME: Don't hardcode this.
+  static const size_t table_size = 256;
 #endif
   _LIBCPP_HIDE_FROM_ABI const mask* table() const _NOEXCEPT { return __tab_; }
   static const mask* classic_table() _NOEXCEPT;

libcxx/include/__locale

@@ -585,7 +585,7 @@ public:
 #  ifdef _CACHED_RUNES
   static const size_t table_size = _CACHED_RUNES;
 #  else
-  static const size_t table_size = 256; // FIXME: Don't hardcode this.
+  static const size_t table_size = 256;
 #  endif
   _LIBCPP_HIDE_FROM_ABI const mask* table() const _NOEXCEPT { return __tab_; }
   static const mask* classic_table() _NOEXCEPT;