Revert "Added tests for os/mac/keg"

Revert "mach: Avoid reopening the file for relocation"

Revert "keg_relocate: use correct number of arguments in call to change_install_name"

Added tests for os/mac/keg

keg_relocate: use correct number of arguments in call to change_install_name

During the changes to macho file relocation refactoring
in #3101, #3138, and #3139,
the number of arguments to the mach::change_install_name
function changed from 3 to 2, but
there was still an instance of the function being called
with the wrong number of arguments.

bump-formula-pr: fix duplicates check

`return unless pull_requests && !pull_requests.empty?` and
`return unless pull_requests&.empty?` are not equivalent.

mach: Avoid reopening the file for relocation

This commit allows the relocation code to perform install name
and dylib ID changes without reopening the file separately.

Rubocop: 0.50.0 and Ruby 2.3

portable-ruby: use rebuild with coverage support.

portable-ruby: fix installation on Leopard.

This will allow `simplecov` to generate coverage by rebuilding portable
Ruby with coverage support.

README: add Commsworld logo.

They host our physical hardware.

Download it insecurely there and require `rubygems` for `Gem::Version`.

vendor-install: output only to stderr.

This avoids causing errors in scripts that call e.g. `brew --prefix`.

utils/git: cache less aggressively.

This should avoid weird test ordering failures with specs on Linux (but
there's no real reason this can't occur on macOS too).

audit: also skip homebrew/science duplicates found by search_taps

Follow-up to #3202.

audit: don't check for homebrew/science duplicates

It's just noise to turn the migration PRs red over expected duplicates.

utils/git: don't fail when CoreTap is untapped.

This produces test failures on Linux where we intentionally avoid having
it tapped.

audit: hack around El Capitan audit failure.

popen: Do not suppress stderr when HOMEBREW_STDERR

portable-ruby: improve installation messaging.