Remove alloc_clear

Use `xcalloc` instead.
Inline `alloc_tv` and `alloc_string_tv` in eval.c

src/memory.c

@@ -53,14 +53,6 @@ char_u *alloc(unsigned size)
   return lalloc((long_u)size, TRUE);
 }
 
-/*
- * Allocate memory and set all bytes to zero.
- */
-char_u *alloc_clear(unsigned size)
-{
-  return (char_u *)xcalloc(1, (size_t)size);
-}
-
 /// Try to free memory. Used when trying to recover from out of memory errors.
 /// @see {xmalloc}
 static void try_to_free_memory()