build: drop "async" feature

Cargo.toml

@@ -32,7 +32,7 @@ unindent = { version = "0.2.1", optional = true }
 inventory = { version = "0.3.0", optional = true }
 
 # coroutine implementation
-futures-task = { version = "0.3", optional = true }
+futures-task = "0.3"
 
 # crate integrations that can be added using the eponymous features
 anyhow = { version = "1.0", optional = true }
@@ -64,9 +64,7 @@ futures = "0.3.28"
 pyo3-build-config = { path = "pyo3-build-config", version = "0.20.0", features = ["resolve-config"] }
 
 [features]
-default = ["async", "macros"]
-
-async = ["futures-task", "macros"]
+default = ["macros"]
 
 # Enables pyo3::inspect module and additional type information on FromPyObject
 # and IntoPy traits
@@ -106,7 +104,6 @@ nightly = []
 # This is mostly intended for testing purposes - activating *all* of these isn't particularly useful.
 full = [
     "macros",
-    "async",
     # "multiple-pymethods", # TODO re-add this when MSRV is greater than 1.62
     "chrono",
     "num-bigint",