Use git describe to get the HOMEBREW_VERSION.

For tagged commits produces the output:
- `1.0.1`

For untagged commits with a dirty tree produces the output:
- `1.0.1-19-g23efbc5-dirty`

Performance:
```
git describe --tags --dirty 2> /dev/null
0.07s user 0.01s system 96% cpu 0.086 total
```

This means we can tag any commit without needing to manually remember
to bump the revision every time.

1 files changed, 0 insertions, 9 deletions

diff --git a/Library/Homebrew/utils.rb b/Library/Homebrew/utils.rb
index e466f8a08..be629f1df 100644
--- a/Library/Homebrew/utils.rb
+++ b/Library/Homebrew/utils.rb
@@ -248,15 +248,6 @@ module Homebrew
     _system(cmd, *args)
   end
 
-  def self.homebrew_version_string
-    if pretty_revision = HOMEBREW_REPOSITORY.git_short_head
-      last_commit = HOMEBREW_REPOSITORY.git_last_commit_date
-      "#{HOMEBREW_VERSION} (git revision #{pretty_revision}; last commit #{last_commit})"
-    else
-      "#{HOMEBREW_VERSION} (no git repository)"
-    end
-  end
-
   def self.core_tap_version_string
     require "tap"
     tap = CoreTap.instance