Remove rpm-plugin-ima in Dockerfile on F41

This plugin of ours, when installed in a container, currently causes
transaction errors (simply because IMA isn't supported in containers
currently).

This isn't immediately visible unless another dnf transaction would be
run, either in the Dockerfile itself, or in a custom podman container
made from the resulting "rpm" image tag.  Note that the tests themselves
aren't affected by this since they currently don't install any
IMA-signed packages.

In any case, the systemw-wide plugin is unnecessary in the test image,
make sure to remove it.

The reason it's installed is through the ima-evm-utils-devel package
(which pulls in ima-evm-utils-libs which pulls in the plugin).  This is
a new thing on F41 so only handle it there.

tests/Dockerfile.fedora

@@ -64,7 +64,11 @@ RUN ln -sf $(rpm --eval '%{_target_platform}%{?_gnu}')-pkg-config \
            /usr/bin/pkg-config
 
 # Self-destruct stock rpm
-RUN if ! which dnf5; then \
+RUN if which dnf5; then \
+        # Fedora 41+ \
+        rpm -e --nodeps --nodb \
+            rpm-plugin-ima; \
+    else \
         # Fedora 40 \
         rpm -e --nodeps --nodb \
             rpm-sign-libs \