Revert "Deprecate strings/slices functions covered by stdlib slices"

This reverts commit 4965b0f as it
incorrectly started using stdlib slices without declaring that this repo
is now only compatible with golang >=1.21.

strings/slices/slices.go

@@ -20,14 +20,21 @@ limitations under the License.
 // replace "stringslices" if the "slices" package becomes standard.
 package slices
 
-import goslices "slices"
-
 // Equal reports whether two slices are equal: the same length and all
 // elements equal. If the lengths are different, Equal returns false.
 // Otherwise, the elements are compared in index order, and the
 // comparison stops at the first unequal pair.
-// Deprecated: use [slices.Equal] instead.
-var Equal = goslices.Equal[[]string, string]
+func Equal(s1, s2 []string) bool {
+	if len(s1) != len(s2) {
+		return false
+	}
+	for i, n := range s1 {
+		if n != s2[i] {
+			return false
+		}
+	}
+	return true
+}
 
 // Filter appends to d each element e of s for which keep(e) returns true.
 // It returns the modified d. d may be s[:0], in which case the kept
@@ -44,14 +51,32 @@ func Filter(d, s []string, keep func(string) bool) []string {
 }
 
 // Contains reports whether v is present in s.
-// Deprecated: use [slices.Contains] instead.
-var Contains = goslices.Contains[[]string, string]
+func Contains(s []string, v string) bool {
+	return Index(s, v) >= 0
+}
 
 // Index returns the index of the first occurrence of v in s, or -1 if
 // not present.
-// Deprecated: use [slices.Index] instead.
-var Index = goslices.Index[[]string, string]
+func Index(s []string, v string) int {
+	// "Contains" may be replaced with "Index(s, v) >= 0":
+	// https://github.com/golang/go/issues/45955#issuecomment-873377947
+	for i, n := range s {
+		if n == v {
+			return i
+		}
+	}
+	return -1
+}
+
+// Functions below are not in https://github.com/golang/go/issues/45955
 
 // Clone returns a new clone of s.
-// Deprecated: use [slices.Clone] instead.
-var Clone = goslices.Clone[[]string, string]
+func Clone(s []string) []string {
+	// https://github.com/go101/go101/wiki/There-is-not-a-perfect-way-to-clone-slices-in-Go
+	if s == nil {
+		return nil
+	}
+	c := make([]string, len(s))
+	copy(c, s)
+	return c
+}