Replace API standalone functions due to TypeScript update

It turns out that you can no longer stub free-standing functions in Typescript 3.9.2+ according to this issue:

microsoft/TypeScript#38568
sinonjs/sinon#562

Author: natalynyu

src/client/components/pages/__tests__/CourseAdmin.test.tsx

@@ -16,7 +16,7 @@ import {
   stub,
   SinonStub,
 } from 'sinon';
-import * as courseAPI from 'client/api/courses';
+import { CourseAPI } from 'client/api/courses';
 import {
   computerScienceCourseResponse,
   physicsCourseResponse,
@@ -58,7 +58,7 @@ describe('Course Admin', function () {
     newAreaCourseResponse,
   ];
   beforeEach(function () {
-    getStub = stub(courseAPI, 'getAllCourses');
+    getStub = stub(CourseAPI, 'getAllCourses');
     getStub.resolves(testData);
     dispatchMessage = stub();
   });

src/client/components/pages/__tests__/FacultyAdmin.test.tsx

@@ -10,7 +10,7 @@ import {
   stub,
   SinonStub,
 } from 'sinon';
-import * as facultyAPI from 'client/api/faculty';
+import { FacultyAPI } from 'client/api/faculty';
 import {
   physicsFacultyMemberResponse,
   bioengineeringFacultyMemberResponse,
@@ -30,7 +30,7 @@ describe('Faculty Admin', function () {
     newAreaFacultyMemberResponse,
   ];
   beforeEach(function () {
-    getStub = stub(facultyAPI, 'getAllFacultyMembers');
+    getStub = stub(FacultyAPI, 'getAllFacultyMembers');
     dispatchMessage = stub();
     getStub.resolves(testData);
   });