[UpdateTestChecks] Remove outdated help text

[nikic]

Summary

Manually modifying the result of update_test_checks.py is discouraged, we prefer unmodified check lines where possible. The output is also considered authoritative nowadays, at least for tests targeting core middle-end components, where not using it is an automatic review rejection.

[RKSimon]

LGTM

llvm/utils/update_test_checks.py

3. Update the RUN-lines in the affected regression tests to look canonical.
    Example: "; RUN: opt < %s -instcombine -S | FileCheck %s"
 4. Refresh the FileCheck lines for either the entire file or select functions by
    running this script.
 5. Commit the fresh baseline of checks.
 6. Apply your patch from step 1 and rebuild your local binaries.
 7. Re-run this script on affected regression tests.
 8. Check the diffs to ensure the script has done something reasonable.
 9. Submit a patch including the regression test diffs for review.
-
-A common pattern is to have the script insert complete checking of every
-instruction. Then, edit it down to only check the relevant instructions.
-The script is designed to make adding checks to a test case fast, it is *not*
-designed to be authoratitive about what constitutes a good test!
 """
 
 from __future__ import print_function
 
 import argparse
 import os  # Used to advertise this file's name ("autogenerated_note").
 import re
 import sys