delete unused module

it will likely be back at some point, but not worth worrying about for
now.

src/akh_source_map.erl

@@ -1,21 +0,0 @@
--module(akh_source_map).
--include("akh_source_map.hrl").
--export([
-    empty/0,
-    insert/3,
-    get_loc/2
-]).
-
--spec empty() -> source_map().
-empty() -> gb_trees:empty().
-
--spec insert(Offset :: non_neg_integer(), Line :: pos_integer(), source_map()) ->
-    source_map().
-insert(Offset, Line, SourceMap) -> gb_trees:insert(Offset, Line, SourceMap).
-
--spec get_loc(Offset :: non_neg_integer(), source_map()) -> #loc{}.
-get_loc(Offset, SourceMap) ->
-    case gb_trees:smaller(Offset, SourceMap) of
-        {Start, Line} -> #loc{line = Line, col = Offset - Start - 1};
-        none -> #loc{line = 0, col = Offset}
-    end.

src/akh_source_map.hrl

@@ -1,5 +0,0 @@
--type source_map() :: gb_trees:tree(non_neg_integer(), pos_integer()).
-
--type span() :: {non_neg_integer(), pos_integer()}.
-
--record(loc, {line :: pos_integer(), col :: non_neg_integer()}).