Clean up linker script symbols

src/hello/hello.d

@@ -13,7 +13,9 @@ import hulk.memory;
 import ldc.llvmasm;
 
 __gshared EFI_SYSTEM_TABLE * st;
+/** HULK binary start address, 4KB-aligned. */
 extern extern(C) __gshared ubyte _hulk_bin_start;
+/** HULK binary end address, 4KB-aligned. */
 extern extern(C) __gshared ubyte _hulk_bin_end;
 private align(4096) __gshared ubyte[1024 * 1024] scratch_buffer;
 /** Index to the memory map region being used to allocate page tables. */
@@ -39,14 +41,9 @@ private ulong hulk_bin_size()
     return cast(ulong)&_hulk_bin_end - cast(ulong)&_hulk_bin_start;
 }
 
-private ulong hulk_total_size()
-{
-    return cast(ulong)hulk_header().total_size;
-}
-
 private ulong hulk_bss_size()
 {
-    return hulk_total_size() - hulk_bin_size();
+    return cast(ulong)hulk_header().hulk_bss_size;
 }
 
 private ulong hulk_stack_size()