ww: lib tests run via -T test mode; bare mains retired (closes @test conversion)

'ww test' gains the istest build path (-T injection in build_one/
buildone) and do_test/dotest accept -I, mirroring do_run - both twins.
The 35 converted lib tests drop their interim bare mains (-T
synthesizes the entry from @test fns and rejects a user main); their
35 C run-drivers flip 'ww run' -> 'ww test'; 989_lib_byteid compiles
lib tests under -T (8 user-main probe fixtures stay non-T, gated on
the fixture field). Abort-on-first-failure stands until the deferred
record-and-continue harness lands with the multi-package arc.

lib/ww/asttest.ww

@@ -100,8 +100,3 @@ fn checkname(k: nkind, want: str) void = {
 	// named value (68); 69 is out of band, exercising the "?" tail.
 	checkname(69: nkind, "?");
 };
-
-export fn main() i32 = {
-	nkname_cases();
-	return 0;
-};

lib/ww/lex/toktest.ww

@@ -307,11 +307,3 @@ fn checkfloat(src: str, want: u64) void = {
 	checkfloat("1.0e308", 0x7FE1CCF385EBC8A0u64);
 	checkfloat("2.225073858507202e-308", 0x0010000000000001u64);
 };
-
-export fn main() i32 = {
-	tokname_cases();
-	kwlookup_cases();
-	tokprint_cases();
-	floatfold_cases();
-	return 0;
-};