Trim some unused deps from wasmtime-environ (#1515)

Was poking around but looks like these are no longer needed

Cargo.lock

@@ -1395,7 +1395,7 @@ dependencies = [
  "rand_isaac",
  "rand_jitter",
  "rand_os",
- "rand_pcg 0.1.2",
+ "rand_pcg",
  "rand_xorshift",
  "winapi",
 ]
@@ -1411,7 +1411,6 @@ dependencies = [
  "rand_chacha 0.2.2",
  "rand_core 0.5.1",
  "rand_hc 0.2.0",
- "rand_pcg 0.2.1",
 ]
 
 [[package]]
@@ -1520,15 +1519,6 @@ dependencies = [
  "rand_core 0.4.2",
 ]
 
-[[package]]
-name = "rand_pcg"
-version = "0.2.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "16abd0c1b639e9eb4d7c50c0b8100b0d0f849be2349829c740fe8e6eb4816429"
-dependencies = [
- "rand_core 0.5.1",
-]
-
 [[package]]
 name = "rand_xorshift"
 version = "0.1.1"
@@ -2212,11 +2202,9 @@ dependencies = [
  "log",
  "more-asserts",
  "pretty_env_logger",
- "rand 0.7.3",
  "rayon",
  "serde",
  "sha2",
- "target-lexicon",
  "tempfile",
  "thiserror",
  "toml",