Deprecate redundant error type ConnectError

The two error types look like this, side by side:
```zig
pub const RequestError = ConnectTcpError || error{
    UnsupportedUriScheme,
    UriMissingHost,
    UriHostTooLong,
    CertificateBundleLoadFailure,
};
pub const ConnectError = ConnectTcpError || RequestError;
```

Once evaluated, then end up containing the exact same error types, so it
is redundant to have them both. I chose to keep `RequestError` because
it is used slightly more and also so the `Client.request()` method gets
an error return type that matches the name of the method.

Author: joshua-holmes

lib/std/http/Client.zig

@@ -1063,7 +1063,7 @@ pub const Request = struct {
         try w.writeAll("\r\n");
     }
 
-    pub const ReceiveHeadError = http.Reader.HeadError || ConnectError || error{
+    pub const ReceiveHeadError = http.Reader.HeadError || RequestError || error{
         /// Server sent headers that did not conform to the HTTP protocol.
         ///
         /// To find out more detailed diagnostics, `http.Reader.head_buffer` can be
@@ -1562,7 +1562,8 @@ pub fn connectProxied(
     };
 }
 
-pub const ConnectError = ConnectTcpError || RequestError;
+/// Deprecated. Please use `RequestError` instead.
+pub const ConnectError = RequestError;
 
 /// Connect to `host:port` using the specified protocol. This will reuse a
 /// connection if one is already open.