Delete code for OS X 10.5 or earlier

delete #if blocks like this:

    #if MAC_OS_X_VERSION_MAX_ALLOWED <= MAC_OS_X_VERSION_10_4
      :
    #endif

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2539 f4f36d40-9719-0410-9868-dde021a23eda
Delete file "objc_compat.h" for OS X 10.4 or earlier

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2540 f4f36d40-9719-0410-9868-dde021a23eda