Remove dependency to pkg-config.

pkg-config is useless for this simple use. Removing it allows to build most SRs 3 times faster.

component/libxslt/buildout.cfg

 [buildout]
 extends =
   ../libxml2/buildout.cfg
-  ../pkgconfig/buildout.cfg
   ../zlib/buildout.cfg
 
 parts =
@@ -19,7 +18,5 @@ configure-options =
   --without-debug
   --without-debugger
 environment =
-  PATH=${pkgconfig:location}/bin:%(PATH)s
-  CPPFLAGS=-I${zlib:location}/include
-  LDFLAGS=-Wl,-rpath=${zlib:location}/lib
-  PKG_CONFIG_PATH=${libxml2:location}/lib/pkgconfig:${zlib:location}/lib/pkgconfig
+  CPPFLAGS=-I${zlib:location}/include -I${libxml2:location}/include 
+  LDFLAGS=-L${libxml2:location}/lib -Wl,-rpath=${libxml2:location}/lib -L${zlib:location}/lib -Wl,-rpath=${zlib:location}/lib