Both packages referred to the same repo (`gflags/gflags` at GitHub),
both packages used almost the same version (2.2.1 and 2.2.0). Therefore
I think that it's just fair to drop one of the packages to avoid
duplication and reduce the maintenance overload.
I decided to drop `gflags` originally packaged by @shlevy as it didn't
contain testing support as `google-gflags` does. The package set refers
from `gflags` to `google-gflags`, so both package names remain (to avoid
any confusions), however the `gflags` expression is removed.
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