Move dead_code related tests to test/ui/dead-code

This helps organize the tests better.  I also renamed several of the tests to remove redundant dead-code in the path, and better match what they're testing

Author: Quantumplation

src/test/ui/dead-code-alias-in-pat.rs renamed to src/test/ui/lint/dead-code/alias-in-pat.rs

@@ -1,11 +1,11 @@
 error: function is never used: `foo`
-  --> $DIR/fail-no-dead-code.rs:4:1
+  --> $DIR/basic.rs:4:1
    |
 LL | fn foo() {
    | ^^^^^^^^
    |
 note: lint level defined here
-  --> $DIR/fail-no-dead-code.rs:1:9
+  --> $DIR/basic.rs:1:9
    |
 LL | #![deny(dead_code)]
    |         ^^^^^^^^^

src/test/ui/lint-dead-code-associated-type.rs renamed to src/test/ui/lint/dead-code/associated-type.rs

@@ -1,11 +1,11 @@
 error: enum is never used: `E`
-  --> $DIR/lint-dead-code-empty-unused-enum.rs:3:1
+  --> $DIR/empty-unused-enum.rs:3:1
    |
 LL | enum E {}
    | ^^^^^^
    |
 note: lint level defined here
-  --> $DIR/lint-dead-code-empty-unused-enum.rs:1:9
+  --> $DIR/empty-unused-enum.rs:1:9
    |
 LL | #![deny(unused)]
    |         ^^^^^^