Remove //@ compare-output-lines-by-subset directive (#2151)

Author: jieyouxu

Diff for: src/tests/directives.md

@@ -94,7 +94,6 @@ for more details.
 | `check-run-results`               | Check run test binary `run-{pass,fail}` output snapshot                                                                  | `ui`, `crashes`, `incremental` if `run-pass` | N/A                                                                                     |
 | `error-pattern`                   | Check that output contains a regex pattern                                                                               | `ui`, `crashes`, `incremental` if `run-pass` | Regex                                                                                   |
 | `check-stdout`                    | Check `stdout` against `error-pattern`s from running test binary[^check_stdout]                                          | `ui`, `crashes`, `incremental`               | N/A                                                                                     |
-| `compare-output-lines-by-subset`  | Check output contains the contents of the snapshot by lines opposed to checking for strict equality                      | `ui`, `coverage`                             | N/A                                                                                     |
 | `normalize-stderr-32bit`          | Normalize actual stderr (for 32-bit platforms) with a rule `"<raw>" -> "<normalized>"` before comparing against snapshot | `ui`, `incremental`                          | `"<RAW>" -> "<NORMALIZED>"`, `<RAW>`/`<NORMALIZED>` is regex capture and replace syntax |
 | `normalize-stderr-64bit`          | Normalize actual stderr (for 64-bit platforms) with a rule `"<raw>" -> "<normalized>"` before comparing against snapshot | `ui`, `incremental`                          | `"<RAW>" -> "<NORMALIZED>"`, `<RAW>`/`<NORMALIZED>` is regex capture and replace syntax |
 | `normalize-stderr-test`           | Normalize actual stderr with a rule `"<raw>" -> "<normalized>"` before comparing against snapshot                        | `ui`, `incremental`                          | `"<RAW>" -> "<NORMALIZED>"`, `<RAW>`/`<NORMALIZED>` is regex capture and replace syntax |

Diff for: src/tests/ui.md

@@ -89,9 +89,6 @@ will check for output files:
   [Normalization](#normalization)).
 - `dont-check-compiler-stderr` — Ignores stderr from the compiler.
 - `dont-check-compiler-stdout` — Ignores stdout from the compiler.
-- `compare-output-lines-by-subset` — Checks that the output contains the
-  contents of the stored output files by lines opposed to checking for strict
-  equality.
 
 UI tests run with `-Zdeduplicate-diagnostics=no` flag which disables rustc's
 built-in diagnostic deduplication mechanism. This means you may see some