kbuild: doc: remove "Objects which export symbols" section

EXPORT_SYMBOL is unrelated to makefiles. No need to mention it.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Documentation/kbuild/makefiles.rst

@@ -12,7 +12,7 @@ This document describes the Linux kernel Makefiles.
 	   --- 3.1 Goal definitions
 	   --- 3.2 Built-in object goals - obj-y
 	   --- 3.3 Loadable module goals - obj-m
-	   --- 3.4 Objects which export symbols
+	   --- 3.4 <deleted>
 	   --- 3.5 Library file goals - lib-y
 	   --- 3.6 Descending down in directories
 	   --- 3.7 Non-builtin vmlinux targets - extra-y
@@ -247,12 +247,6 @@ more details, with real examples.
 	kbuild will build an ext2.o file for you out of the individual
 	parts and then link this into built-in.a, as you would expect.
 
-3.4 Objects which export symbols
---------------------------------
-
-	No special notation is required in the makefiles for
-	modules exporting symbols.
-
 3.5 Library file goals - lib-y
 ------------------------------