libdpkg: Move compression command name macros from header to C file

These are private macros, so there's no point in exporting them.

lib/dpkg/compress.c

@@ -132,6 +132,8 @@ static const struct compressor compressor_none = {
  * Gzip compressor.
  */
 
+#define GZIP		"gzip"
+
 static void
 fixup_gzip_params(struct compress_params *params)
 {
@@ -250,6 +252,8 @@ static const struct compressor compressor_gzip = {
  * Bzip2 compressor.
  */
 
+#define BZIP2		"bzip2"
+
 static void
 fixup_bzip2_params(struct compress_params *params)
 {
@@ -373,6 +377,8 @@ static const struct compressor compressor_bzip2 = {
  * Xz compressor.
  */
 
+#define XZ		"xz"
+
 static bool
 check_xz_params(struct compress_params *params, struct dpkg_error *err)
 {

lib/dpkg/compress.h

@@ -29,10 +29,6 @@
 
 DPKG_BEGIN_DECLS
 
-#define GZIP		"gzip"
-#define XZ		"xz"
-#define BZIP2		"bzip2"
-
 enum compressor_type {
 	compressor_type_unknown = -1,
 	compressor_type_none,