Remove some remnants of Ruby 1.8.7 support

xcode: reduce minimum CLT version.

This should be 1.0.0 to be nicer to 10.7 users.

Fixes #1893.

audit: exempt wine's deps from the universal deprecation

Since this hack is no longer required, and `Emoji.tick` and `.cross` are
only called in one place, I think it's better to just inline them there
rather than having methods on `Emoji` that just return a one-character
String.

tests: automatically restore ENV in teardown

Fix installer deleting artifacts if they already exist.

Add internal command to calculate appcast checkpoint.

Cask: cleanups internal stanzas

This was deprecated and had all formulae removed in:
https://github.com/Homebrew/homebrew-gui/pull/52

Remove legacy cask cache instead of migrating.

Suggested by @reitermarkus in
https://github.com/Homebrew/brew/pull/1890#discussion_r97234536, and
then I added the \A and \Z.

bottle: fix regex

A common git environment is now used in all tests, so this is no longer
required.

This will allow the `brew bundle` test to use the default git
environment.

See https://github.com/Homebrew/brew/pull/1890#discussion_r97229473.

Proposed by @reitermarkus in
https://github.com/Homebrew/brew/pull/1890#discussion_r97210285.

I made one slight adjustment of preserving the previous date string in
case anything was relying on it.

I was waiting for confirmation that there wasn't a good reason for these
to be stubbed before I removed them.

tests: clean up file system for all tests

Noted that this is intended for the revision of this formula instead of
rebuild of a bottle.