all: update LZMA SDK license information

The LZMA SDK was placed in the public domain as of
version 4.62 (December 2008).

  https://www.7-zip.org/sdk.html

And according to https://sourceforge.net/p/sevenzip/discussion/45797/thread/685169cf/

  "Are older LZMA versions in the public domain?"
  "Yes, you can use old versions of LZMA SDK as public domain."
    -- Igor Pavlov, 2011-06-21

src/help.cpp

@@ -471,7 +471,7 @@ void show_version(bool one_line) {
     fprintf(f, "Copyright (C) 1995" "-2024 Jean-loup Gailly and Mark Adler\n");
 #endif
 #if (WITH_LZMA)
-    // see vendor/lzma-sdk/lzma.txt
+    // see vendor/lzma-sdk
     fprintf(f, "Copyright (C) 1999" "-2006 Igor Pavlov\n");
 #endif
 #if (WITH_ZSTD)