Remove _mesa_memcpy in favor of plain memcpy.

This may break the SUNOS4 build, but it's no longer relevant.
diff --git a/src/mesa/shader/program.c b/src/mesa/shader/program.c
index 18ef6d5..3bf9a65 100644
--- a/src/mesa/shader/program.c
+++ b/src/mesa/shader/program.c
@@ -223,7 +223,7 @@
       p++;
    len = p - lineStart;
    s = (GLubyte *) _mesa_malloc(len + 1);
-   _mesa_memcpy(s, lineStart, len);
+   memcpy(s, lineStart, len);
    s[len] = 0;
 
    return s;