Cargo.toml: Remove "doc" feature

It was largely a hack to support *ring*'s slightly incompatible ECDSA
signing interface without polluting the docs.

We hopefully don't need it anymore.

.circleci/config.yml

@@ -62,12 +62,6 @@ jobs:
           rustc --version
           cargo --version
           cargo build --features=usb --release
-    - run:
-        name: build --features=doc
-        command: |
-          rustc --version
-          cargo --version
-          cargo build --features=doc
     - run:
         name: test
         command: |

Cargo.toml

@@ -44,7 +44,6 @@ ring = "0.13"
 untrusted = "0.6"
 
 [features]
-doc = ["mockhsm", "rsa", "usb"]
 default = ["http", "passwords"]
 http = []
 mockhsm = ["passwords", "ring", "untrusted"]
@@ -54,7 +53,7 @@ rsa = ["sha2"]
 usb = ["lazy_static", "libusb"]
 
 [package.metadata.docs.rs]
-features = ["doc"]
+all-features = true
 rustc-args = ["-Ctarget-feature=+aes"]
 
 [[bench]]