Remove memcpy prototypes at Russ' request to prevent code from calling

memcpy directly.

defs.h

@@ -124,7 +124,6 @@ void            popcli();
 // string.c
 int             memcmp(const void*, const void*, uint);
 void*           memmove(void*, const void*, uint);
-void*           memcpy(void*, const void*, uint);
 void*           memset(void*, int, uint);
 char*           safestrcpy(char*, const char*, int);
 int             strlen(const char*);

string.c

@@ -44,6 +44,7 @@ memmove(void *dst, const void *src, uint n)
   return dst;
 }
 
+// memcpy exists to placate GCC.  Use memmove.
 void*
 memcpy(void *dst, const void *src, uint n)
 {

user.h

@@ -26,7 +26,6 @@ int sleep(int);
 int stat(char*, struct stat*);
 char* strcpy(char*, char*);
 void *memmove(void*, void*, int);
-void *memcpy(void*, void*, int);
 char* strchr(const char*, char c);
 int strcmp(const char*, const char*);
 void printf(int, char*, ...);