[packaging] Update mocks for rpmbuilder mock format

The Puppet Labs mocks created by rpmbuilder have assumed a new format, pl-el-*
vs el-*, in order to avoid overwriting the configurations supplied by the mock
package. This commit updates the mocks in dashboard to reflect the new
standard, so that we can continue to build packages with builders created with
the rpmbuilder module. It also removes the RC mocks, which are no longer used
in the packaging repo or in the module.

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>