Makefile: remove "libnm.actions" explicitly when uninstalling

On Fedora 33 when compiling NetworkManager it is failing with the
following error:

```
ERROR: files left in build directory after distclean:
./docs/libnm/libnm.actions
make[1]: *** [Makefile:18427: distcleancheck] Error 1
make[1]: Leaving directory '/builddir/nm-build/NetworkManager/NetworkManager-1.27.90/_build/sub'
make: *** [Makefile:18356: distcheck] Error 1
Error make distcheck
```

Adding the file to the DISTCLEANFILES will enforce the removal of this
file.

Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
21 jobs for fix_distclean in 34 minutes and 54 seconds (queued for 4 seconds)
latest
Status Job ID Name Coverage
  Test
passed #5188993
checkpatch

00:02:38

manual #5189001
allowed to fail manual
t_centos:7.5.1804
manual #5189002
allowed to fail manual
t_centos:7.6.1810
manual #5189003
allowed to fail manual
t_centos:7.7.1908
manual #5189004
allowed to fail manual
t_centos:7.8.2003
manual #5189005
allowed to fail manual
t_centos:8.1.1911
manual #5189011
allowed to fail manual
t_debian:10
manual #5189010
allowed to fail manual
t_debian:9
manual #5189013
allowed to fail manual
t_debian:sid
manual #5189012
allowed to fail manual
t_debian:testing
manual #5188994
allowed to fail manual
t_fedora:28
manual #5188995
allowed to fail manual
t_fedora:29
manual #5188996
allowed to fail manual
t_fedora:30
manual #5188997
allowed to fail manual
t_fedora:31
passed #5188998
t_fedora:32

00:34:54

manual #5188999
allowed to fail manual
t_fedora:33
manual #5189000
allowed to fail manual
t_fedora:rawhide
manual #5189006
allowed to fail manual
t_ubuntu:16.04
manual #5189007
allowed to fail manual
t_ubuntu:18.04
manual #5189009
allowed to fail manual
t_ubuntu:devel
manual #5189008
allowed to fail manual
t_ubuntu:rolling