Misconfiguration of the CUDA solver for Ceres

[Bob-Eric]

Ceres' CUDA solver supports only three dense solvers, which require the else statement to be removed. Otherwise it will fall back to the default SPARSE_NORMAL_CHOLESKY linear solver, resulting in higher CPU usage. https://github.com/zinuok/VINS-Fusion-ROS2/blob/af78d13438064b856622f2ca65c5dae4fcc0f54a/vins/src/estimator/estimator.cpp#L1171