The 1840 edition accidentally deleted the thus here in Alma 57:4. This change is not due to editing since no other instances of thus were ever deleted in the 1840 edition. Moreover, there would have been no motivation for deleting the thus here. The 1908 RLDS edition restored the original thus to the RLDS text.
Summary: Maintain the thus in Alma 57:4; the deletion of this particular thus in the 1840 edition was not due to Joseph Smith’s editing but was simply a typo.