Remove snipMate compatibility script.

The engine does not use this and it should therefore live in
vim-snippets.

plugin/snipMate_compatibility.vim

@@ -1,15 +0,0 @@
-if exists('did_UltiSnips_snipmate_compatibility')
-       finish
-endif
-let did_UltiSnips_snipmate_compatibility = 1
-
-if ! exists('g:snips_author')
-       let g:snips_author = "John Doe"
-endif
-
-" Filename function, taken from snipMate.vim
-fun! Filename(...)
-    let filename = expand('%:t:r')
-    if filename == '' | return a:0 == 2 ? a:2 : '' | endif
-    return !a:0 || a:1 == '' ? filename : substitute(a:1, '$1', filename, 'g')
-endf