Mppx: don't restore cookies after invocation
Mppx: don't restore cookies after invocation

Ppx are invoked only once so there is no need to manage cookies and, as
pointed by @lpw25, restoring cookies cause the load path to be scanned.
This doubles the number of uncached calls to stat which can be expensive
on large projects.

rgrinberg/merlin,the-lambda-church/merlin,rgrinberg/merlin,ocaml/merlin,dra27/merlin,the-lambda-church/merlin,rgrinberg/merlin,the-lambda-church/merlin,rgrinberg/merlin,dra27/merlin,ocaml/merlin,dra27/merlin,ocaml/merlin,dra27/merlin,ocaml/merlin