[memory.syn] Remove redundant freestanding mark for members

Making `allocator_arg_t` shown like `from_range_t` in [ranges.syn].

Author: frederick-vs-ja

source/memory.tex

@@ -104,9 +104,7 @@
 	                                      size_t n) noexcept;
 
   // \ref{allocator.tag}, allocator argument tag
-  struct allocator_arg_t {                                                          // freestanding
-      explicit allocator_arg_t() = default;                                         // freestanding
-  };
+  struct allocator_arg_t { explicit allocator_arg_t() = default; };                 // freestanding
   inline constexpr allocator_arg_t allocator_arg{};                                 // freestanding
 
   // \ref{allocator.uses}, \tcode{uses_allocator}