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.

(cherry picked from commit 2c2ed3272b992b6eb13864e49847c943e42be00f)

src/core/exec-credential.c

@@ -378,8 +378,6 @@ static int load_credential_glob(
                                         ownership_ok,
                                         data, size,
                                         left);
-                        if (r == -EEXIST)
-                                continue;
                         if (r < 0)
                                 return r;
                 }