delete some seemingly redundant code

We're patching line_cache and then immediately clearing it using
Text.redraw_all.

edit.lua

@@ -440,7 +440,6 @@ function edit.keychord_press(State, chord, key)
       State.cursor1 = deepcopy(src.cursor)
       State.selection1 = deepcopy(src.selection)
       patch(State.lines, event.after, event.before)
-      patch_placeholders(State.line_cache, event.after, event.before)
       -- invalidate various cached bits of lines
       State.lines.current_drawing = nil
       Text.redraw_all(State)  -- if we're scrolling, reclaim all line caches to avoid memory leaks

source_edit.lua

@@ -441,7 +441,6 @@ function edit.keychord_press(State, chord, key)
       State.cursor1 = deepcopy(src.cursor)
       State.selection1 = deepcopy(src.selection)
       patch(State.lines, event.after, event.before)
-      patch_placeholders(State.line_cache, event.after, event.before)
       -- invalidate various cached bits of lines
       State.lines.current_drawing = nil
       Text.redraw_all(State)  -- if we're scrolling, reclaim all line caches to avoid memory leaks

source_undo.lua

@@ -81,17 +81,6 @@ function patch(lines, from, to)
   end
 end
 
-function patch_placeholders(line_cache, from, to)
-  assert(from.start_line == to.start_line, 'failed to patch undo operation')
-  for i=from.end_line,from.start_line,-1 do
-    table.remove(line_cache, i)
-  end
-  assert(#to.lines == to.end_line-to.start_line+1, 'failed to patch undo operation')
-  for i=1,#to.lines do
-    table.insert(line_cache, to.start_line+i-1, {})
-  end
-end
-
 -- https://stackoverflow.com/questions/640642/how-do-you-copy-a-lua-table-by-value/26367080#26367080
 function deepcopy(obj, seen)
   if type(obj) ~= 'table' then return obj end

undo.lua

@@ -81,17 +81,6 @@ function patch(lines, from, to)
   end
 end
 
-function patch_placeholders(line_cache, from, to)
-  assert(from.start_line == to.start_line, 'failed to patch undo operation')
-  for i=from.end_line,from.start_line,-1 do
-    table.remove(line_cache, i)
-  end
-  assert(#to.lines == to.end_line-to.start_line+1, 'failed to patch undo operation')
-  for i=1,#to.lines do
-    table.insert(line_cache, to.start_line+i-1, {})
-  end
-end
-
 -- https://stackoverflow.com/questions/640642/how-do-you-copy-a-lua-table-by-value/26367080#26367080
 function deepcopy(obj, seen)
   if type(obj) ~= 'table' then return obj end