[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/parse_test.go

@@ -0,0 +1,103 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestParseTreeEntriesLong(t *testing.T) {
+	testCases := []struct {
+		Input    string
+		Expected []*TreeEntry
+	}{
+		{
+			Input: `100644 blob ea0d83c9081af9500ac9f804101b3fd0a5c293af    8218	README.md
+100644 blob 037f27dc9d353ae4fd50f0474b2194c593914e35    4681	README_ZH.md
+100644 blob 9846a94f7e8350a916632929d0fda38c90dd2ca8     429	SECURITY.md
+040000 tree 84b90550547016f73c5dd3f50dea662389e67b6d       -	assets
+`,
+			Expected: []*TreeEntry{
+				{
+					ID:        MustIDFromString("ea0d83c9081af9500ac9f804101b3fd0a5c293af"),
+					name:      "README.md",
+					entryMode: EntryModeBlob,
+					size:      8218,
+					sized:     true,
+				},
+				{
+					ID:        MustIDFromString("037f27dc9d353ae4fd50f0474b2194c593914e35"),
+					name:      "README_ZH.md",
+					entryMode: EntryModeBlob,
+					size:      4681,
+					sized:     true,
+				},
+				{
+					ID:        MustIDFromString("9846a94f7e8350a916632929d0fda38c90dd2ca8"),
+					name:      "SECURITY.md",
+					entryMode: EntryModeBlob,
+					size:      429,
+					sized:     true,
+				},
+				{
+					ID:        MustIDFromString("84b90550547016f73c5dd3f50dea662389e67b6d"),
+					name:      "assets",
+					entryMode: EntryModeTree,
+					sized:     true,
+				},
+			},
+		},
+	}
+	for _, testCase := range testCases {
+		entries, err := ParseTreeEntries([]byte(testCase.Input))
+		require.NoError(t, err)
+		assert.Len(t, entries, len(testCase.Expected))
+		for i, entry := range entries {
+			assert.EqualValues(t, testCase.Expected[i], entry)
+		}
+	}
+}
+
+func TestParseTreeEntriesShort(t *testing.T) {
+	testCases := []struct {
+		Input    string
+		Expected []*TreeEntry
+	}{
+		{
+			Input: `100644 blob ea0d83c9081af9500ac9f804101b3fd0a5c293af	README.md
+040000 tree 84b90550547016f73c5dd3f50dea662389e67b6d	assets
+`,
+			Expected: []*TreeEntry{
+				{
+					ID:        MustIDFromString("ea0d83c9081af9500ac9f804101b3fd0a5c293af"),
+					name:      "README.md",
+					entryMode: EntryModeBlob,
+				},
+				{
+					ID:        MustIDFromString("84b90550547016f73c5dd3f50dea662389e67b6d"),
+					name:      "assets",
+					entryMode: EntryModeTree,
+				},
+			},
+		},
+	}
+	for _, testCase := range testCases {
+		entries, err := ParseTreeEntries([]byte(testCase.Input))
+		require.NoError(t, err)
+		assert.Len(t, entries, len(testCase.Expected))
+		for i, entry := range entries {
+			assert.EqualValues(t, testCase.Expected[i], entry)
+		}
+	}
+}
+
+func TestParseTreeEntriesInvalid(t *testing.T) {
+	// there was a panic: "runtime error: slice bounds out of range" when the input was invalid: #20315
+	entries, err := ParseTreeEntries([]byte("100644 blob ea0d83c9081af9500ac9f804101b3fd0a5c293af"))
+	require.Error(t, err)
+	assert.Empty(t, entries)
+}