Remove TrustedLen requirement from BuilderMethods::switch

The main use case of TrustedLen is allowing APIs to specialize on it,
but no use of it uses that specialization. Instead, only the .len()
function provided by ExactSizeIterator is used, which is already
required to be accurate.

Thus, the TrustedLen requirement on BuilderMethods::switch is redundant.

compiler/rustc_codegen_llvm/src/lib.rs

@@ -12,7 +12,6 @@
 #![feature(in_band_lifetimes)]
 #![feature(nll)]
 #![feature(or_patterns)]
-#![feature(trusted_len)]
 #![recursion_limit = "256"]
 
 use back::write::{create_informational_target_machine, create_target_machine};