Fuzzer action: redundant control flow wrapping

[MattWindsor91]

This is a catch-all issue for any fuzzer actions that take a statement S and wrap it in a control flow that is guaranteed to execute once and only once.

This could be:

• an if statement with an always-true guard;
• a do... while loop with an always-false guard;
• a while or for loop engineered to break after one iteration (eg, while true or for (;;) with a break, though this'll need care to avoid optimisation

[MattWindsor91]

Done (in if and do…while flavours).