fixup: use \brk{} to avoid overfull hbox and remove comment

Co-authored-by: Jan Schultke <[email protected]>

Author: dietmarkuehl

source/exec.tex

@@ -6491,7 +6491,7 @@
 parameter following the first \tcode{allocator_arg_t} parameter (if
 any) and let \tcode{alloc} be \tcode{Allocator(arg_next)}.  Then
 \tcode{PAlloc} is \tcode{allocator_traits<Allocator>::template
-rebind_alloc\linebreak<U>} where \tcode{U} is an unspecified type % avoid Overfull
+re\-bind_alloc\brk{}<U>} where \tcode{U} is an unspecified type
 whose size and alignment are both \tcode{__STDCPP_DEFAULT_NEW_ALIGNMENT__}.
 
 \pnum