refactor: remove file token feature

Problem: The file metadata token (file:<path>:<line>) was implemented
but is no longer wanted.

Solution: Remove all traces — parse.lua token parsing, diff.lua
reconciliation, views.lua LineMeta field, buffer.lua virtual text and
PendingFile highlight, complete.lua omnifunc trigger, init.lua
goto_file/add_here functions and -file edit token, plugin keymaps
<Plug>(pending-goto-file) and <Plug>(pending-add-here), config.lua
goto_file keymap field, vimdoc FILE TOKEN section, and
spec/file_spec.lua.

lua/pending/complete.lua

@@ -124,7 +124,6 @@ function M.omnifunc(findstart, base)
       { vim.pesc(dk) .. ':([%S]*)$', dk },
       { 'cat:([%S]*)$', 'cat' },
       { vim.pesc(rk) .. ':([%S]*)$', rk },
-      { 'file:([%S]*)$', 'file' },
     }
 
     for _, check in ipairs(checks) do