manual: remove suggestion of aligning = signs in .mk files

It is not buildroot convention to align the = signs in .mk files, so this
shouldn't be suggested in the manual.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

docs/manual/writing-rules.txt

@@ -71,13 +71,7 @@ LIBFOO_VERSION = 1.0
 LIBFOO_CONF_OPT += --without-python-support
 ---------------------
 +
-It is also possible to align the +=+ signs:
-+
----------------------
-LIBFOO_VERSION   = 1.0
-LIBFOO_SOURCE    = foo-$(LIBFOO_VERSION).tar.gz
-LIBFOO_CONF_OPT += --without-python-support
----------------------
+Do not align the +=+ signs.
 
 * Indentation: use tab only:
 +