Remove -Zreport-delayed-bugs.

It's not used within the repository in any way (e.g. in tests), and
doesn't seem useful.

compiler/rustc_session/src/config.rs

@@ -1162,7 +1162,6 @@ impl UnstableOptions {
             can_emit_warnings,
             treat_err_as_bug: self.treat_err_as_bug,
             dont_buffer_diagnostics: self.dont_buffer_diagnostics,
-            report_delayed_bugs: self.report_delayed_bugs,
             macro_backtrace: self.macro_backtrace,
             deduplicate_diagnostics: self.deduplicate_diagnostics,
             track_diagnostics: self.track_diagnostics,

compiler/rustc_session/src/options.rs

@@ -1841,8 +1841,6 @@ options! {
     remark_dir: Option<PathBuf> = (None, parse_opt_pathbuf, [UNTRACKED],
         "directory into which to write optimization remarks (if not specified, they will be \
 written to standard error output)"),
-    report_delayed_bugs: bool = (false, parse_bool, [TRACKED],
-        "immediately print bugs registered with `span_delayed_bug` (default: no)"),
     sanitizer: SanitizerSet = (SanitizerSet::empty(), parse_sanitizers, [TRACKED],
         "use a sanitizer"),
     sanitizer_cfi_canonical_jump_tables: Option<bool> = (Some(true), parse_opt_bool, [TRACKED],