Remove unused `TlsError::Webpki` error variant

The error variant is no longer needed since `rustls` 0.21.

Cargo.toml

@@ -24,7 +24,7 @@ native-tls = ["native-tls-crate"]
 native-tls-vendored = ["native-tls", "native-tls-crate/vendored"]
 rustls-tls-native-roots = ["__rustls-tls", "rustls-native-certs"]
 rustls-tls-webpki-roots = ["__rustls-tls", "webpki-roots"]
-__rustls-tls = ["rustls", "webpki"]
+__rustls-tls = ["rustls"]
 
 [dependencies]
 data-encoding = { version = "2", optional = true }
@@ -52,11 +52,6 @@ version = "0.21.0"
 optional = true
 version = "0.6.0"
 
-[dependencies.webpki]
-optional = true
-version = "0.22"
-features = ["std"]
-
 [dependencies.webpki-roots]
 optional = true
 version = "0.23"

src/error.rs

@@ -271,10 +271,6 @@ pub enum TlsError {
     #[cfg(feature = "__rustls-tls")]
     #[error("rustls error: {0}")]
     Rustls(#[from] rustls::Error),
-    /// Webpki error.
-    #[cfg(feature = "__rustls-tls")]
-    #[error("webpki error: {0}")]
-    Webpki(#[from] webpki::Error),
     /// DNS name resolution error.
     #[cfg(feature = "__rustls-tls")]
     #[error("Invalid DNS name")]