Remove workaround for failure that's now gone

Cargo.lock

@@ -279,28 +279,6 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
-[[package]]
-name = "failure"
-version = "0.1.8"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d32e9bd16cc02eae7db7ef620b392808b89f6a5e16bb3497d159c6b92a0f4f86"
-dependencies = [
- "backtrace",
- "failure_derive",
-]
-
-[[package]]
-name = "failure_derive"
-version = "0.1.8"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "aa4da3c766cd7a0db8242e326e9e4e081edd567072893ed320008189715366a4"
-dependencies = [
- "proc-macro2",
- "quote",
- "syn 1.0.109",
- "synstructure",
-]
-
 [[package]]
 name = "fastrand"
 version = "2.0.2"
@@ -450,7 +428,6 @@ dependencies = [
  "bufstream",
  "chrono",
  "encoding",
- "failure",
  "imap-proto",
  "lazy_static",
  "lettre",
@@ -1055,18 +1032,6 @@ dependencies = [
  "unicode-ident",
 ]
 
-[[package]]
-name = "synstructure"
-version = "0.12.6"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f36bdaa60a83aca3921b5259d5400cbf5e90fc51931376a9bd4a0eb79aa7210f"
-dependencies = [
- "proc-macro2",
- "quote",
- "syn 1.0.109",
- "unicode-xid",
-]
-
 [[package]]
 name = "tempfile"
 version = "3.10.1"
@@ -1150,12 +1115,6 @@ version = "0.1.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e51733f11c9c4f72aa0c160008246859e340b00807569a0da0e7a1079b27ba85"
 
-[[package]]
-name = "unicode-xid"
-version = "0.2.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f962df74c8c05a667b5ee8bcf162993134c104e96440b663c8daa176dc772d8c"
-
 [[package]]
 name = "untrusted"
 version = "0.9.0"

Cargo.toml

@@ -41,7 +41,6 @@ structopt = "0.3"
 # to make -Zminimal-versions work
 [target.'cfg(any())'.dependencies]
 encoding = { version = "0.2.32", optional = true }
-failure = { version = "0.1.8", optional = true }
 mime = { version = "0.3.4", optional = true }
 openssl = { version = "0.10.60", optional = true }
 openssl-macros = { version = "0.1.1", optional = true }