std: Remove generics from Option::expect

This commit removes the <M: Any + Send> type parameter from Option::expect in
favor of just taking a hard-coded `&str` argument. This allows this function to
move into libcore.

Previous code using strings with `expect` will continue to work, but code using
this implicitly to transmit task failure will need to unwrap manually with a
`match` statement.

[breaking-change]
Closes #14008

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libstd/rt/env.rs b/src/libstd/rt/env.rs
index c9e5cae60e4..7271464d1e9 100644
--- a/src/libstd/rt/env.rs
+++ b/src/libstd/rt/env.rs
@@ -11,7 +11,7 @@
 //! Runtime environment settings
 
 use from_str::from_str;
-use option::{Some, None, Expect};
+use option::{Some, None};
 use os;
 use str::Str;