Conflicting entries for glibmm

[Martin Michel]

Hi Guix experts,

I have a strange problem which I cannot resolve. I wanted to install
gtksourceviewmm but it failed due to conflicting entries for glibmm.
However, glibmm seems not to be properly installed, I cannot remove it
and a `--list-installed` of `guix package` showed no results.

Can you help me how to solve this situation and properly install
gtksourceviewmm from scratch?

```
$ guix install gtksourceviewmm
The following package will be installed:
   gtksourceviewmm 3.18.0

guix install: error: profile contains conflicting entries for glibmm
guix install: error:   first entry: glibmm@2.70.0 
/gnu/store/fpfi5y405y04rpiz7zn75gmiilwkzb4x-glibmm-2.70.0
guix install: error:    ... propagated from gtksourceviewmm@3.18.0
guix install: error:   second entry: glibmm@2.64.5 
/gnu/store/0sl7zf5bcr1qb7yfq2wqqly1w3x0spn8-glibmm-2.64.5
guix install: error:    ... propagated from pangomm@2.46.0
guix install: error:    ... propagated from gtkmm@3.24.5
guix install: error:    ... propagated from gtksourceviewmm@3.18.0
hint: You cannot have two different versions or variants of `gtksourceviewmm' 
in the same profile.

$ guix remove glibmm
guix remove: error: package 'glibmm' not found in profile
```

Thanks in advance for your hints!

Kind regards,
Martin