Use portable_simd from std instead of packed_simd

Since this seems to be the way forward and they encourage using the
feature flag instead of the using it as a separate crate.

Cargo.lock

@@ -281,7 +281,6 @@ name = "diopser"
 version = "0.1.0"
 dependencies = [
  "nih_plug",
- "packed_simd_2",
 ]
 
 [[package]]
@@ -465,12 +464,6 @@ dependencies = [
  "winapi",
 ]
 
-[[package]]
-name = "libm"
-version = "0.1.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7fc7aa29613bd6a620df431842069224d8bc9011086b1db4c0e0cd47fa03ec9a"
-
 [[package]]
 name = "lock_api"
 version = "0.4.6"
@@ -644,16 +637,6 @@ dependencies = [
  "ttf-parser",
 ]
 
-[[package]]
-name = "packed_simd_2"
-version = "0.3.7"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "defdcfef86dcc44ad208f71d9ff4ce28df6537a4e0d6b0e8e845cb8ca10059a6"
-dependencies = [
- "cfg-if",
- "libm",
-]
-
 [[package]]
 name = "parking_lot"
 version = "0.12.0"