Spotted by Chris Forbes:
* `std::remove_if` wasn't introduced in C++20, it's been there since 98. I just can't read docs.
* Also fix the lack of `list.erase()`.

Bug: None. drive-by-code-reviewing-fixes.
Change-Id: I456d540ba973640747d6e4cb23faec65a4a9c83d
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/43348
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Ben Clayton <bclayton@google.com>