[CHORE] Drop go-git support

See https://codeberg.org/forgejo/discussions/issues/164 for the
rationale and discussion of this change.

Everything related to the `go-git` dependency is dropped (Only a single
instance is left in a test file to test for an XSS, it requires crafting
an commit that Git itself refuses to craft). `_gogit` files have
been removed entirely, `go:build: !gogit` is removed, `XXX_nogogit.go` files
either have been renamed or had their code being merged into the
`XXX.go` file.

modules/git/last_commit_cache.go

@@ -4,6 +4,7 @@
 package git
 
 import (
+	"context"
 	"crypto/sha256"
 	"fmt"
 
@@ -112,3 +113,47 @@ func (c *LastCommitCache) GetCommitByPath(commitID, entryPath string) (*Commit,
 
 	return lastCommit, nil
 }
+
+// CacheCommit will cache the commit from the gitRepository
+func (c *Commit) CacheCommit(ctx context.Context) error {
+	if c.repo.LastCommitCache == nil {
+		return nil
+	}
+	return c.recursiveCache(ctx, &c.Tree, "", 1)
+}
+
+func (c *Commit) recursiveCache(ctx context.Context, tree *Tree, treePath string, level int) error {
+	if level == 0 {
+		return nil
+	}
+
+	entries, err := tree.ListEntries()
+	if err != nil {
+		return err
+	}
+
+	entryPaths := make([]string, len(entries))
+	for i, entry := range entries {
+		entryPaths[i] = entry.Name()
+	}
+
+	_, err = WalkGitLog(ctx, c.repo, c, treePath, entryPaths...)
+	if err != nil {
+		return err
+	}
+
+	for _, treeEntry := range entries {
+		// entryMap won't contain "" therefore skip this.
+		if treeEntry.IsDir() {
+			subTree, err := tree.SubTree(treeEntry.Name())
+			if err != nil {
+				return err
+			}
+			if err := c.recursiveCache(ctx, subTree, treeEntry.Name(), level-1); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}