Doc/Makefile: don't build Makefile.build man

This is developers documentation, I doubt any user of crui
is interested in that. So let's not build it by default.

It can still be built manually:

make -C Documentation Makefile.build.1
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

Documentation/Makefile

@@ -5,7 +5,6 @@ A2X		:= a2x
 XMLTO		:= xmlto
 
 SRC		+= crtools.txt
-SRC		+= Makefile.build.txt
 MANS		:= $(patsubst %.txt,%.1,$(SRC))
 
 all: $(MANS)