Remove code cell

Author: gregorgorjanc

tskitr.md

@@ -31,7 +31,7 @@ By default, this uses `reticulate`'s isolated Python virtual environment, but
 you can also use another Python environment as described at
 <https://rstudio.github.io/reticulate/>.
 
-```{code-cell}
+```
 install.packages("reticulate")
 reticulate::py_require(c("tskit", "msprime"))
 ```