style: remove unnecessary mut and unsafe keywords

Compiler nagged about these. Remove it to please the compiler.

Author: oherrala

src/lib.rs

@@ -1,5 +1,5 @@
 // Original work Copyright (c) 2014 The Rust Project Developers
-// Modified work Copyright (c) 2016-2017 Nikita Pekin and the lazycell contributors
+// Modified work Copyright (c) 2016-2018 Nikita Pekin and the lazycell contributors
 // See the README.md file at the top-level directory of this distribution.
 //
 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
@@ -63,7 +63,7 @@ impl<T> LazyCell<T> {
     ///
     /// This function will return `Err(value)` is the cell is already full.
     pub fn fill(&self, value: T) -> Result<(), T> {
-        let mut slot = unsafe { &mut *self.inner.get() };
+        let slot = unsafe { &mut *self.inner.get() };
         if slot.is_some() {
             return Err(value);
         }
@@ -135,7 +135,7 @@ impl<T> LazyCell<T> {
 
     /// Consumes this `LazyCell`, returning the underlying value.
     pub fn into_inner(self) -> Option<T> {
-        unsafe { self.inner.into_inner() }
+        self.inner.into_inner()
     }
 }
 
@@ -206,7 +206,7 @@ impl<T> AtomicLazyCell<T> {
 
     /// Consumes this `LazyCell`, returning the underlying value.
     pub fn into_inner(self) -> Option<T> {
-        unsafe { self.inner.into_inner() }
+        self.inner.into_inner()
     }
 }