compress: make Mark.Twain-Tom.Sawyer.txt licensed under non-free license free again

This change strips non-free license from Mark.Twain-Tom.Sawyer.txt along with all reference to Project Gutenberg in the file and the whole source tree. Making the file public domain again.

Fixes #13216

Change-Id: I2f41b0de225f627dde152efe93c006a4c24be668
Reviewed-on: https://go-review.googlesource.com/17196Reviewed-by: Andrew Gerrand <adg@golang.org>

src/compress/bzip2/bzip2_test.go

@@ -181,7 +181,7 @@ var testfiles = []string{
 	// does not repeat, but there are only 10 possible digits, so it should be
 	// reasonably compressible.
 	digits: "testdata/e.txt.bz2",
-	// Twain is Project Gutenberg's edition of Mark Twain's classic English novel.
+	// Twain is Mark Twain's classic English novel.
 	twain: "testdata/Mark.Twain-Tom.Sawyer.txt.bz2",
 	// 16KB of random data from /dev/urandom
 	random: "testdata/random.data.bz2",

src/compress/flate/reader_test.go

@@ -32,7 +32,7 @@ var testfiles = []string{
 	// does not repeat, but there are only 10 possible digits, so it should be
 	// reasonably compressible.
 	digits: "../testdata/e.txt",
-	// Twain is Project Gutenberg's edition of Mark Twain's classic English novel.
+	// Twain is Mark Twain's classic English novel.
 	twain: "../testdata/Mark.Twain-Tom.Sawyer.txt",
 }