Remove unnecessary tests

Since it's a library feature it shouldn't be declared inside the
compiler

Author: eduardorittner

compiler/rustc_feature/src/unstable.rs

@@ -592,8 +592,6 @@ declare_features! (
     (unstable, simd_ffi, "1.0.0", Some(27731)),
     /// Allows specialization of implementations (RFC 1210).
     (incomplete, specialization, "1.7.0", Some(31844)),
-    /// Allows splitting a slice by another slice
-    (unstable, split_pattern, "CURRENT_RUSTC_VERSION", Some(49036)),
     /// Allows attributes on expressions and non-item statements.
     (unstable, stmt_expr_attributes, "1.6.0", Some(15701)),
     /// Allows lints part of the strict provenance effort.

compiler/rustc_span/src/symbol.rs

@@ -1864,7 +1864,6 @@ symbols! {
         soft,
         specialization,
         speed,
-        split_pattern,
         spotlight,
         sqrtf128,
         sqrtf16,