Remove ^L characters hidden randomly in the code. Not those used in text files as delimiters.

While working on a tool that processes Erlang code and testing it against this repo,
I found out about those little sneaky 0xff. I thought it may be of help to other
people build such tools to remove non-conforming-to-standard characters.
Merge branch 'fenollp/treewide_remove_unexpected_0xff/OTP-11323' into maint

* fenollp/treewide_remove_unexpected_0xff/OTP-11323:
  Remove ^L characters hidden randomly in the code. Not those used in text files as delimiters.
Typo fix ambigous -> ambiguous
Rename otp_8949_a/0 which common_test interprets as an info function

Before running a test case named testcase/1, common_test will call
testcase/0 (the info function). Exceptions and illegal return values
would be silently ignored. In a planned update to common_test, errors
will instead cause the test case to fail.

The test case otp_8949_a/1 has a helper function called otp_8949_a/0.
Rename it to do_otp_8949_a/0.

While at it, also fix a copy and paste bug in the list of test cases.
otp_8949_a was run twice; otp_8949_b was never run.
Prepare release