Revert "Reapply "[libc++] Explicitly convert to masks in SIMD code (#107983)"" (#122022)
Reverts llvm/llvm-project#121352
Triggers "vector type should not be a bool!" on:
```
bool a[100];
bool b[100];
auto t = std::mismatch(std::begin(a), std::end(a), std::begin(b), std::end(b));
```
https://godbolt.org/z/Y73s3sdef