delete dead code

kalloc.c

@@ -21,7 +21,7 @@ struct {
 extern char end[]; // first address after kernel loaded from ELF file
 static char *newend;
 
-// simple page allocator to get off the ground during entry
+// A simple page allocator to get off the ground during entry
 char *
 enter_alloc(void)
 {
@@ -36,12 +36,6 @@ enter_alloc(void)
   return p;
 }
 
-uint
-detect_memory(void)
-{
-  return 0xE000000;
-}
-
 // Initialize free list of physical pages.
 void
 kinit(void)