Simplify regression test

Co-authored-by: Joshua Nelson <[email protected]>

Author: teryror

src/test/rustdoc/issue-80893.rs

@@ -1,7 +1,6 @@
-// compile-flags: --test -Z unstable-options --test-builder true --runtool true
+// compile-flags: --test -Z unstable-options --test-builder true
 
-/// ```
-/// This does not compile, but specifying a custom --test-builder should let this pass anyway
-/// `true` does not generate an output file to run, so we also specify it as a runtool
+/// ```no_run
+/// This tests that `--test-builder` is accepted as a flag by rustdoc.
 /// ```
 pub struct Foo;