unskip passing libc++ tests

These tests failed because an iterator claims to be random-access without supporting subtraction, which breaks with our pre-C++20 `_Idl_distance`. C++20-and-later `_Idl_distance` isn't fooled by such shenanigans. (We only test libc++ in `/std:c++latest` mode.)

tests/libcxx/expected_results.txt

@@ -24,10 +24,6 @@ std/time/time.syn/formatter.year_month_weekday.pass.cpp:1 FAIL
 std/time/time.syn/formatter.zoned_time.pass.cpp:0 FAIL
 std/time/time.syn/formatter.zoned_time.pass.cpp:1 FAIL
 
-# LLVM-74756: [libc++][test] overload_compare_iterator doesn't support its claimed iterator_category
-std/utilities/memory/specialized.algorithms/uninitialized.copy/uninitialized_copy.pass.cpp FAIL
-std/utilities/memory/specialized.algorithms/uninitialized.move/uninitialized_move.pass.cpp FAIL
-
 # LLVM-90196: [libc++][format] Formatting range with m range-type is incorrect
 std/utilities/format/format.range/format.range.formatter/format.functions.format.pass.cpp FAIL
 std/utilities/format/format.range/format.range.formatter/format.functions.vformat.pass.cpp FAIL