unnessacary Vec::retain when executing sc.d/w instruction

[lenawanel]

rvemu/src/cpu.rs

Line 1814 in f55eb5b

self.reservation_set.retain(|&x| x != addr);

rvemu/src/cpu.rs

Line 1793 in f55eb5b

self.reservation_set.retain(|&x| x != addr);

both of these lines do nothing, as

rvemu/src/cpu.rs

Line 1786 in f55eb5b

if self.reservation_set.contains(&addr) {

already has shown that addr is not in the reservation set, when reaching these lines.