rPackages.mzR: unpin boost

`mzR` currently ships and builds its own copy of boost-176, see
https://github.com/sneumann/mzR/blob/master/src/README.updateboost

pkgs/development/r-modules/default.nix

@@ -360,7 +360,7 @@ let
     ModelMetrics = lib.optional stdenv.isDarwin pkgs.llvmPackages.openmp;
     mvabund = [ pkgs.gsl ];
     mwaved = [ pkgs.fftw.dev ];
-    mzR = with pkgs; [ zlib boost159.dev netcdf ];
+    mzR = with pkgs; [ zlib netcdf ];
     ncdf4 = [ pkgs.netcdf ];
     nloptr = with pkgs; [ nlopt pkg-config libiconv ];
     n1qn1 = [ pkgs.gfortran ];