Remove CallExpr.getQualifier() and its single, pointless, use.

ql/src/semmle/go/Expr.qll

@@ -444,13 +444,6 @@ class CallExpr extends CallOrConversionExpr {
     )
   }
 
-  /**
-   * Gets the qualifier of this call if it can be determined syntactically.
-   *
-   * For example, in the call `fmt.Println("hello")`, the qualifier is `fmt`.
-   */
-  Expr getQualifier() { calls(result, _) }
-
   /** Gets the `i`th argument expression of this call (0-based). */
   Expr getArgument(int i) {
     i >= 0 and

ql/src/semmle/go/dataflow/internal/DataFlowPrivate.qll

@@ -78,12 +78,6 @@ predicate jumpStep(Node n1, Node n2) {
   )
 }
 
-/**
- * Holds if `call` passes an implicit or explicit qualifier, i.e., a
- * `this` parameter.
- */
-predicate callHasQualifier(CallExpr call) { exists(call.getQualifier()) }
-
 private newtype TContent =
   TFieldContent(Field f) or
   TCollectionContent() or