Don't omit self from uninitialized writes

We can safely create uninitialized writes for `self` variables, because
they appear at index -1 in the entry block of a method, and are
immediately overwritten by a write to `self` at index 0. As a result,
they are not live and will be pruned from the CFG.

Author: hmac

ruby/ql/lib/codeql/ruby/dataflow/internal/SsaImpl.qll

@@ -7,8 +7,7 @@ private import CfgNodes::ExprNodes
 /** Holds if `v` is uninitialized at index `i` in entry block `bb`. */
 predicate uninitializedWrite(EntryBasicBlock bb, int i, LocalVariable v) {
   v.getDeclaringScope() = bb.getScope() and
-  i = -1 and
-  not v instanceof SelfVariable
+  i = -1
 }
 
 /** Holds if `bb` contains a caputured read of variable `v`. */