apply ^github.com optimization for all instances

The purpose of this change is to remove a special-case for Sourcegraph.com.

If a user's query has a repo filter like `repo:github.com/foo`, we rewrite it to `repo:^github.com/foo` (note the `^`). This makes the DB query faster because it only needs to search at the beginning of the string.

This optimization only happens on Sourcegraph.com because technically someone could have a repo at (say) `https://github.com/owner/foo.github.com` or `https://myothercodehost.example.com/foo.github.com/bar`, and they could query `repo:github.com` intending to match one of those. We wanted to avoid that behavior on customer instances. Those are rare edge cases, and the user could work around this rewriting with `repo:.*github.com` if truly needed. We now make this rewriting only occur if there is a trailing slash, which mitigates the (anyway likely zero) impact.

Making this rewriting behavior consistent removes a dotcom edge case and could improve repository search performance for common queries with a tiny hypothetical impact on the behavior.

Note that GitHub Pages repositories are not affected here because those are named `foo.github.io` not `foo.github.com` (https://docs.github.com/en/pages/getting-started-with-github-pages/creating-a-github-pages-site#creating-a-repository-for-your-site).

Author: sqs

internal/search/repos/BUILD.bazel

@@ -15,7 +15,6 @@ go_library(
         "//internal/api",
         "//internal/conf",
         "//internal/database",
-        "//internal/dotcom",
         "//internal/endpoint",
         "//internal/gitserver",
         "//internal/gitserver/gitdomain",

internal/search/repos/repos.go

@@ -22,7 +22,6 @@ import (
 	"github.com/sourcegraph/sourcegraph/internal/api"
 	"github.com/sourcegraph/sourcegraph/internal/conf"
 	"github.com/sourcegraph/sourcegraph/internal/database"
-	"github.com/sourcegraph/sourcegraph/internal/dotcom"
 	"github.com/sourcegraph/sourcegraph/internal/endpoint"
 	"github.com/sourcegraph/sourcegraph/internal/gitserver"
 	"github.com/sourcegraph/sourcegraph/internal/gitserver/gitdomain"
@@ -1117,7 +1116,7 @@ func findPatternRevs(includePatterns []query.ParsedRepoFilter) (outputPatterns [
 }
 
 func optimizeRepoPatternWithHeuristics(repoPattern string) string {
-	if dotcom.SourcegraphDotComMode() && (strings.HasPrefix(repoPattern, "github.com") || strings.HasPrefix(repoPattern, `github\.com`)) {
+	if strings.HasPrefix(repoPattern, "github.com/") || strings.HasPrefix(repoPattern, `github\.com/`) {
 		repoPattern = "^" + repoPattern
 	}
 	// Optimization: make the "." in "github.com" a literal dot