Drop EEXIST handling in load_credential_glob()

Credentials are written to a temporary file and renamed to the
destination with renameat() which will replace existing files so
EEXIST should not happen so drop the handling for EEXIST.

src/core/exec-credential.c

@@ -442,8 +442,6 @@ static int load_credential_glob(
                                         ownership_ok,
                                         data, size,
                                         left);
-                        if (r == -EEXIST)
-                                continue;
                         if (r < 0)
                                 return r;
                 }