Remove explicit dependency on string-conversions

Signed-off-by: Jan Hamal Dvořák <mordae@anilinux.org>

hikaru.cabal

@@ -82,7 +82,6 @@ common common
       , mtl                >=2.2  && <2.3
       , praha              >=0.1  && <0.2
       , resourcet          >=1.2  && <1.3
-      , string-conversions >=0.4  && <0.5
       , text               >=1.2  && <1.3
       , time               >=1.9  && <1.12
       , unliftio           >=0.2  && <0.3