[cleanup] remove overlays code from generated nix files (#538)

## Summary

This has not been used for many months now...

## How was it tested?

Author: savil

internal/impl/devbox_test.go

@@ -67,7 +67,6 @@ func assertShellPlansMatch(t *testing.T, expected *plansdk.ShellPlan, actual *pl
 	assert := assert.New(t)
 
 	assert.ElementsMatch(expected.DevPackages, actual.DevPackages, "DevPackages should match")
-	assert.ElementsMatch(expected.NixOverlays, actual.NixOverlays, "NixOverlays should match")
 }
 
 func fileExists(path string) bool {

internal/impl/tmpl/development.nix.tmpl

@@ -5,13 +5,6 @@ let
     sha256 = "{{ .NixpkgsInfo.Sha256 }}";
     {{- end }}
   }) {
-    {{- if .NixOverlays }}
-      overlays = [
-      {{- range .NixOverlays }}
-        (import (fetchTarball "{{.}}"))
-      {{ end -}}
-      ];
-    {{- end }}
   };
   {{- range .Definitions}}
     {{.}}

internal/impl/tmpl/shell.nix.tmpl

@@ -5,13 +5,6 @@ let
     sha256 = "{{ .NixpkgsInfo.Sha256 }}";
     {{- end }}
   }) {
-    {{- if .NixOverlays }}
-      overlays = [
-      {{- range .NixOverlays }}
-        (import (fetchTarball "{{.}}"))
-      {{ end -}}
-      ];
-    {{- end }}
   };
   {{- range .Definitions}}
     {{.}}

internal/planner/plansdk/plansdk.go

@@ -33,8 +33,6 @@ type ShellPlan struct {
 	DevPackages []string `cue:"[...string]" json:"dev_packages,omitempty"`
 	// Init hook on shell start. Currently, Nginx and python pip planners need it for shell.
 	ShellInitHook []string `cue:"[...string]" json:"shell_init_hook,omitempty"`
-	// Nix overlays. Currently, Rust needs it for shell.
-	NixOverlays []string `cue:"[...string]" json:"nix_overlays,omitempty"`
 	// Nix expressions. Currently, PHP needs it for shell.
 	Definitions []string `cue:"[...string]" json:"definitions,omitempty"`
 	// GeneratedFiles is a map of name => content for files that should be generated
@@ -54,7 +52,7 @@ type PlannerForPackages interface {
 }
 
 // MergeShellPlans merges multiple Plans into one. The merged plan's packages, definitions,
-// and overlays is the union of the packages, definitions, and overlays of the input plans,
+// and shellInitHooks is the union of the packages, definitions, and shellInitHooks of the input plans,
 // respectively.
 func MergeShellPlans(plans ...*ShellPlan) (*ShellPlan, error) {
 	shellPlan := &ShellPlan{}
@@ -67,7 +65,6 @@ func MergeShellPlans(plans ...*ShellPlan) (*ShellPlan, error) {
 
 	shellPlan.DevPackages = pkgslice.Unique(shellPlan.DevPackages)
 	shellPlan.Definitions = pkgslice.Unique(shellPlan.Definitions)
-	shellPlan.NixOverlays = pkgslice.Unique(shellPlan.NixOverlays)
 	shellPlan.ShellInitHook = pkgslice.Unique(shellPlan.ShellInitHook)
 
 	return shellPlan, nil

internal/planner/plansdk/plansdk_test.go

@@ -14,7 +14,6 @@ func TestMergeShellPlans(t *testing.T) {
 	plan2 := &ShellPlan{
 		DevPackages:   []string{},
 		Definitions:   []string{"a"},
-		NixOverlays:   []string{"b"},
 		ShellInitHook: []string{"a", "b"},
 		GeneratedFiles: map[string]string{
 			"a": "b",
@@ -28,18 +27,15 @@ func TestMergeShellPlans(t *testing.T) {
 	// Test merge array
 	plan1 = &ShellPlan{
 		Definitions:   []string{"a"},
-		NixOverlays:   []string{"b"},
 		ShellInitHook: []string{"c"},
 	}
 	plan2 = &ShellPlan{
 		Definitions:   []string{"a"},
-		NixOverlays:   []string{"a"},
 		ShellInitHook: []string{"a", "b"},
 	}
 	expected = &ShellPlan{
 		DevPackages:   []string{},
 		Definitions:   []string{"a"},
-		NixOverlays:   []string{"b", "a"},
 		ShellInitHook: []string{"c", "a", "b"},
 	}
 	actual, err = MergeShellPlans(plan1, plan2)
@@ -63,7 +59,6 @@ func TestMergeShellPlans(t *testing.T) {
 	expected = &ShellPlan{
 		DevPackages:   []string{},
 		Definitions:   []string{},
-		NixOverlays:   []string{},
 		ShellInitHook: []string{},
 		GeneratedFiles: map[string]string{
 			"a": "b",