CmtSet: Remove the emap part (#1235)
CmtSet: Remove the emap part (#1235)

CmtSet.t holds data about a set of comments, accessible either by start
or by end position.

When profiling `ocamlformat`, I noticed that we are spending a lot of
time in the `Map.partitioni_tf` part (10% common, 25% in `js_source.ml`,
can be higher in specially crafted files like `js_source.ml`
concatenated 10 times).

But the `emap` component is never used. It can be safely removed,
yielding a nice performance boost.
ocaml-ppx/ocamlformat,ocaml-ppx/ocamlformat,ocaml-ppx/ocamlformat