Revert last commit, VPATH is necessary for out-of-tree builds.

Originally committed as revision 6014 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/Makefile

+-include ../config.mak
+
+VPATH=$(SRC_PATH)/doc
+
 all: ffmpeg-doc.html faq.html ffserver-doc.html ffplay-doc.html hooks.html \
      ffmpeg.1 ffserver.1 ffplay.1
 

vhook/Makefile

 include ../config.mak
 
+VPATH=$(SRC_PATH)/vhook
+
 CFLAGS=$(VHOOKCFLAGS) -I.. -I$(SRC_PATH) -I$(SRC_PATH)/libavformat \
        -I$(SRC_PATH)/libavcodec -I$(SRC_PATH)/libavutil -DHAVE_AV_CONFIG_H