Configure: stop polluting NGX_ namespace.

While there, fix the only test that used alternative variable name.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

auto/include

@@ -45,9 +45,6 @@ if [ -x $NGX_AUTOTEST ]; then
 
     eval "NGX_INCLUDE_$ngx_name='#include <$ngx_include>'"
 
-    #STUB
-    eval "NGX_$ngx_name='#include <$ngx_include>'"
-
 else
     echo " not found"