test: remove package-wide import assumptions

lib/encoding/base64/base64_test.ww

@@ -13,7 +13,6 @@ import bytes;
 import errors;
 import io;
 import memio;
-import strings;
 import test;
 
 

lib/getopt/getopt_test.ww

@@ -21,7 +21,6 @@ package getopt_test;
 import getopt;
 import io;
 import memio;
-import strings;
 
 fn streq(a: str, b: str) bool = {
 	if (a.len != b.len) { return false; };

lib/strings/utf8_test.ww

@@ -6,7 +6,6 @@
 package strings_test;
 
 import strings;
-import encoding.utf8;
 
 // ref/hare/strings/utf8.ha:31. Validation-half coverage lives in
 // lib/encoding/utf8 (utf8test) per CLAUDE.md rule 9 carve-out.