[builder] Remove undocumented handling of DIST_* environment variables replacements (#13493)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
Remove undocumented handling of `DIST_*` environment variables
replacements

<!-- Issue number if applicable -->
#### Link to tracking issue
Fixes #13335

Author: atoulme

.chloggen/remove_dist_handling.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: builder
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Remove undocumented handling of `DIST_*` environment variables replacements
+
+# One or more tracking issues or pull requests related to the change
+issues: [13335]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

cmd/builder/internal/command.go

@@ -5,7 +5,6 @@ package internal // import "go.opentelemetry.io/collector/cmd/builder/internal"
 
 import (
 	"fmt"
-	"strings"
 
 	"github.com/knadh/koanf/parsers/yaml"
 	"github.com/knadh/koanf/providers/env/v2"
@@ -116,14 +115,7 @@ func initConfig(flags *flag.FlagSet) (*builder.Config, error) {
 	}
 
 	// handle env variables
-	if err = k.Load(env.Provider(".", env.Opt{
-		TransformFunc: func(key string, value string) (string, any) {
-			// Only values from the `dist.` group can be set,
-			// and the subfields in `dist.` contain `_` in their names.
-			// All other fields are arrays and the koanf env provider doesn't provide a straightforward way to set arrays.
-			return strings.Replace(strings.ToLower(key), "dist_", "dist.", 1), value
-		},
-	}), nil); err != nil {
+	if err = k.Load(env.Provider(".", env.Opt{}), nil); err != nil {
 		return nil, fmt.Errorf("failed to load environment variables: %w", err)
 	}