Remove note of test failures on FAT that were fixed by perl #21442's fixes

The list of tests fixed doesn't exactly match the list in README.win32, but
all tests now pass when building/testing on FAT with the Windows OS on NTFS.
Obituary for Greg McCarroll.
patchlevel: we are a release candidate no more!
update v5.20.0 release date in perlhist
update v5.20.0 release date in Module::CoreList
skip RC tags when checking versions diffs
bump version to 5.21.0
new perldelta
add a 5.21 feature bundle
add 5.21.0 to corelist, bump version
regen META.json
do the version bumping and associated 5.21.0-ification
add the 5.20.0 release epigraph
remove CGI.pm from core perl distribution
remove Module-Build from core perl distribution
remove Package-Constants from core perl distribution
match Module::CoreList version to perl version
update corelist for 5.21.0
update perldelta for 5.21.0
fix version in autogenerated acknowledgements