grafana: remove scripts/go to fix go 1.15 build failure

Using subPackages to avoid building this directory would be more
idiomatic but then we would lose the majority of the go tests.

pkgs/servers/monitoring/grafana/default.nix

@@ -25,6 +25,12 @@ buildGoModule rec {
       --replace 'var version = "5.0.0"'  'var version = "${version}"'
   '';
 
+  # fixes build failure with go 1.15:
+  # main module (github.com/grafana/grafana) does not contain package github.com/grafana/grafana/scripts/go
+  preBuild = ''
+    rm -rf scripts/go
+  '';
+
   postInstall = ''
     tar -xvf $srcStatic
     mkdir -p $out/share/grafana

pkgs/top-level/all-packages.nix

@@ -16503,9 +16503,7 @@ in
 
   gofish = callPackage ../servers/gopher/gofish { };
 
-  grafana = callPackage ../servers/monitoring/grafana {
-    buildGoModule = buildGo114Module;
-  };
+  grafana = callPackage ../servers/monitoring/grafana { };
 
   grafana-loki = callPackage ../servers/monitoring/loki {
     buildGoPackage = buildGo114Package;