Revert "Merge branch 'staging-next'"

This reverts commit 41af38f372, reversing
changes made to f0fec244ca.

Let's delay this.  We have some serious regressions.

pkgs/development/r-modules/default.nix

@@ -325,7 +325,7 @@ let
     rmatio = [ pkgs.zlib.dev ];
     Rmpfr = [ pkgs.gmp pkgs.mpfr.dev ];
     Rmpi = [ pkgs.openmpi ];
-    RMySQL = [ pkgs.zlib pkgs.libmysqlclient pkgs.openssl.dev ];
+    RMySQL = [ pkgs.zlib pkgs.mysql.connector-c pkgs.openssl.dev ];
     RNetCDF = [ pkgs.netcdf pkgs.udunits ];
     RODBCext = [ pkgs.libiodbc ];
     RODBC = [ pkgs.libiodbc ];
@@ -810,7 +810,7 @@ let
     });
 
     RMySQL = old.RMySQL.overrideDerivation (attrs: {
-      MYSQL_DIR="${pkgs.libmysqlclient}";
+      MYSQL_DIR=pkgs.mysql.connector-c;
       preConfigure = ''
         patchShebangs configure
       '';