buildroot: don't explicitly add CAP_MAC_ADMIN

This is a left-over from the time when `systemd-nspawn` was used,
which only retained a limited set of capabilities which did not
include `CAP_MAC_ADMIN`[1]. Bubblewrap, on the other hand, retains
all currently capabilities if the process is run as root[2].

[1] see e.g. src/nspawn/nspawn.c#L147 of commit c52950c
[2] see commit abc56644566a6095bb72a5bf70fcee7dd90e9447

osbuild/buildroot.py

@@ -265,7 +265,6 @@ class BuildRoot(contextlib.AbstractContextManager):
 
         cmd = [
             "bwrap",
-            "--cap-add", "CAP_MAC_ADMIN",
             "--chdir", "/",
             "--die-with-parent",
             "--new-session",