removed use of have_memmv.c and HAVE_MEMMOVE, prep for version 2.15.1.2

Removed use of HAVE_MEMMOVE as well have_memmv.c.  Removed the
building and including of have_memmv.h.  Removed the memmove()
function in blkcpy.c, used when HAVE_MEMMOVE was NOT defined.
The libc memmove(3) function as defined by <string.h> is now
required to compile calc because the replacement code in
blkcpy.c q was problematic, especially when regions overlap.
The HAVE_MEMMOVE make symbol was removed from Makefile.config.
Thanks to GitHub user @skeeto for reporting this problem.

alloc.h

@@ -1,7 +1,7 @@
 /*
  * alloc - storage allocation and storage debug macros
  *
- * Copyright (C) 1999-2007,2014  David I. Bell
+ * Copyright (C) 1999-2007,2014,2025  David I. Bell
  *
  * Calc is open software; you can redistribute it and/or modify it under
  * the terms of the version 2.1 of the GNU Lesser General Public License
@@ -32,13 +32,11 @@
 # include "decl.h"
 # include "have_newstr.h"
 # include "have_string.h"
-# include "have_memmv.h"
 # include "have_const.h"
 #else
 # include <calc/decl.h>
 # include <calc/have_newstr.h>
 # include <calc/have_string.h>
-# include <calc/have_memmv.h>
 # include <calc/have_const.h>
 #endif
 
@@ -79,15 +77,4 @@ E_FUNC int strcmp();
 #define strchr(s, c) index(s, c)
 #endif /* HAVE_NEWSTR */
 
-#if !defined(HAVE_MEMMOVE)
-# undef MEMMOVE_SIZE_T
-#if defined(FORCE_STDC) || \
-   (defined(__STDC__) && __STDC__ != 0) || defined(__cplusplus)
-#  define MEMMOVE_SIZE_T size_t
-# else
-#  define MEMMOVE_SIZE_T long
-# endif
-E_FUNC void *memmove(void *s1, CONST void *s2, MEMMOVE_SIZE_T n);
-#endif
-
 #endif /* !INCLUDE_ALLOC_H */