Remove -Z no-opt flag.

Closes #13649

Author: colrdavidson

src/librustc/driver/config.rs

@@ -176,7 +176,6 @@ debugging_opts!(
         SHOW_SPAN,
         COUNT_TYPE_SIZES,
         META_STATS,
-        NO_OPT,
         GC,
         PRINT_LINK_ARGS,
         PRINT_LLVM_PASSES,
@@ -212,7 +211,6 @@ pub fn debugging_opts_map() -> Vec<(&'static str, &'static str, u64)> {
      ("count-type-sizes", "count the sizes of aggregate types",
       COUNT_TYPE_SIZES),
      ("meta-stats", "gather metadata statistics", META_STATS),
-     ("no-opt", "do not optimize, even if -O is passed", NO_OPT),
      ("print-link-args", "Print the arguments passed to the linker",
       PRINT_LINK_ARGS),
      ("gc", "Garbage collect shared data (experimental)", GC),
@@ -714,9 +712,7 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
     let target = matches.opt_str("target").unwrap_or(
         driver::host_triple().to_string());
     let opt_level = {
-        if (debugging_opts & NO_OPT) != 0 {
-            No
-        } else if matches.opt_present("O") {
+        if matches.opt_present("O") {
             if matches.opt_present("opt-level") {
                 early_error("-O and --opt-level both provided");
             }