testimage : remove curl-ptest from rpm index

When creating rpm index for dnf runtime tests, currently all the package
starting with curl are getting included. Now curl-ptest is getting enabled
through another patch but we don't want rpm index to be created for
curl-ptest since it fetches lot of perl dependencies. This patch removes
curl-ptest from rpm index.

Signed-off-by: Yogesh Tyagi <yogesh.tyagi@intel.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>