chore: Remove valgrind suppression for R bindings after updated jsonlite release (#580)

This suppression was annotated "Can be removed when
jeroen/jsonlite#442 is released". This PR can
serve as a placeholder for that until it is released

Author: bkietz

valgrind.supp

@@ -57,12 +57,3 @@
    fun:malloc
    fun:_PyObject_GC_NewVar
 }
-
-# Can be removed when https://github.com/jeroen/jsonlite/pull/442 is released
-{
-   <jsonlite>:Leak in base64_encode
-   Memcheck:Leak
-   ...
-   fun:base64_encode
-   fun:R_base64_encode
-}