Remove gcc, gcc-c++ from private Koji build group

[Anthony Joseph Messina]

In preparation for F29, I went to define new build and srpm-build groups to 
remove gcc an gcc-c++ and remain aligned with Fedora.

However, `koji add-group f29 build` does nothing--it doesn't add the group to 
the database (associated with the f29 tag).  I can also find no errors in the 
Apache or PostgreSQL logs.

It's been a while since I've needed to modify groups which are typically 
inherited from the previous version tag.  Is there something I'm missing?

-- 
Anthony - https://messinet.com
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