Rollup merge of #91185 - camelid:rm-force-overflow-checks, r=wesleywiser

Remove `-Z force-overflow-checks`

It was replaced several years ago by the stable option `-C overflow-checks`.
The goal was to delete the `-Z` flag once users had migrated [1].
Now that it's been several years, it makes sense to delete the old flag.

See also the discussion on Zulip [2].

[1]: https://github.com/rust-lang/rust/issues/33134#issuecomment-280484097
[2]: https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/overflow.20checks/near/262497224

r? ```@wesleywiser```
cc ```@RalfJung```

compiler/rustc_session/src/options.rs

@@ -1131,8 +1131,6 @@ options! {
     fewer_names: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "reduce memory use by retaining fewer names within compilation artifacts (LLVM-IR) \
         (default: no)"),
-    force_overflow_checks: Option<bool> = (None, parse_opt_bool, [TRACKED],
-        "force overflow checks on or off"),
     force_unstable_if_unmarked: bool = (false, parse_bool, [TRACKED],
         "force all crates to be `rustc_private` unstable (default: no)"),
     fuel: Option<(String, u64)> = (None, parse_optimization_fuel, [TRACKED],

compiler/rustc_session/src/session.rs

@@ -678,11 +678,7 @@ impl Session {
         self.opts.debugging_opts.sanitizer.contains(SanitizerSet::CFI)
     }
     pub fn overflow_checks(&self) -> bool {
-        self.opts
-            .cg
-            .overflow_checks
-            .or(self.opts.debugging_opts.force_overflow_checks)
-            .unwrap_or(self.opts.debug_assertions)
+        self.opts.cg.overflow_checks.unwrap_or(self.opts.debug_assertions)
     }
 
     /// Check whether this compile session and crate type use static crt.