Removed XZ compression.

When testing the archlinux, xz compression couldn't seem to extract ANY files.
Testing extraction with the appimage works though. So that's good.

internal/compression/xz.go

@@ -1,47 +0,0 @@
-package compression
-
-import (
-	"bytes"
-	"io"
-
-	"github.com/ulikunitz/xz"
-)
-
-//Xz is a decompressor for xz type compression
-type Xz struct{}
-
-//Decompress reads the entirety of the given reader and returns it uncompressed as a byte slice.
-func (z *Xz) Decompress(r io.Reader) ([]byte, error) {
-	rdr, err := xz.NewReader(r)
-	if err != nil {
-		return nil, err
-	}
-	err = rdr.Verify()
-	if err != nil {
-		return nil, err
-	}
-	var data bytes.Buffer
-	_, err = io.Copy(&data, rdr)
-	if err != nil {
-		return nil, err
-	}
-	return data.Bytes(), nil
-}
-
-//Compress compresses the given data (as a byte array) and returns the compressed data.
-func (z *Xz) Compress(data []byte) ([]byte, error) {
-	var buf bytes.Buffer
-	wrt, err := xz.NewWriter(&buf)
-	if err != nil {
-		return nil, err
-	}
-	defer wrt.Close()
-	_, err = wrt.Write(data)
-	if err != nil {
-		return nil, err
-	}
-	if err != nil {
-		return nil, err
-	}
-	return buf.Bytes(), nil
-}