remove instructions for building on OS X 10.6

The current releases are built on OS X 10.7 and hence these remain
untested -- it is better to document a process which is being used
regularly and is repeatable.

INSTALL.md

@@ -103,15 +103,10 @@ target Windows Vista or later (i.e. NT 6.x) by default.
 OS X
 ----
 
-Building is supported only on OS X 10.6 or newer. You will need to have the
-latest Xcode for your OS X version. Additionally, you will need the command
+Building is supported only on OS X 10.7 or newer. You will need to have the
+latest Xcode for your OS X version. Additionally, you will need to run the command
 `sudo gem install fpm --no-ri --no-rdoc` in the terminal to install
 [fpm](https://github.com/jordansissel/fpm), which is used for building the package.
-Note that if you are using OS X 10.6, you will additionally need to install
-[git 1.8.4.2](https://git-osx-installer.googlecode.com/files/git-1.8.4.2-intel-universal-snow-leopard.dmg)
-and [Python 2.7.6](https://www.python.org/ftp/python/2.7.6/python-2.7.6-macosx10.6.dmg)
-(you may need to run the `Update Shell Profile.command` in `/Applications/Python 2.7`
-to make it the default Python in the shell).
 
 The Carbon build is recommended because it generates PDFs with smaller
 file sizes and selectable text as compared to the Cocoa version, see