[FSSDK-12879] Remove Karma testing infrastructure (#1162)

* Remove Karma testing infrastructure

Karma config files, scripts, and devDependencies are no longer used.
Remove them along with the README reference.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: raju-opti

README.md

@@ -221,7 +221,7 @@ This system is enforced at build time through ESLint rules and validation script
 
 ### Unit Tests
 
-There is a mix of testing paradigms used within the JavaScript SDK which include Mocha, Chai, Karma, and Vitest, indicated by their respective `*.tests.js` and `*.spec.ts` filenames.
+There is a mix of testing paradigms used within the JavaScript SDK which include Mocha, Chai, and Vitest, indicated by their respective `*.tests.js` and `*.spec.ts` filenames.
 
 When contributing code to the SDK, aim to keep the percentage of code test coverage at the current level ([![Coveralls](https://img.shields.io/coveralls/optimizely/javascript-sdk.svg)](https://coveralls.io/github/optimizely/javascript-sdk)) or above.
 
@@ -231,8 +231,8 @@ To run unit tests, you can take the following steps:
 2. Run `npm test` to run all test files.
 3. Run `npm run test-vitest` to run only tests written using Vitest.
 4. Run `npm run test-mocha` to run only tests written using Mocha.
-4. (For cross-browser testing) Run `npm run test-xbrowser` to run tests in many browsers via BrowserStack.
-5. Resolve any tests that fail before continuing with your contribution.
+5. (For cross-browser testing) Run `npm run test-browser-browserstack` to run browser tests via BrowserStack, or `npm run test-browser-local` to run them locally.
+6. Resolve any tests that fail before continuing with your contribution.
 
 This information is relevant only if you plan on contributing to the SDK itself.
 
@@ -243,14 +243,20 @@ npm install
 # Run unit tests.
 npm test
 
-# Run unit tests in many browsers, currently via BrowserStack.
+# Run browser tests locally.
+npm run test-browser-local
+
+# Run browser tests via BrowserStack.
 # For this to work, the following environment variables must be set:
-#   - BROWSER_STACK_USERNAME
-#   - BROWSER_STACK_PASSWORD
-npm run test-xbrowser
+#   - BROWSERSTACK_USERNAME
+#   - BROWSERSTACK_ACCESS_KEY
+npm run test-browser-browserstack
+
+# Run UMD bundle tests via BrowserStack.
+npm run test-umd-browserstack
 ```
 
-[/.github/workflows/javascript.yml](/.github/workflows/javascript.yml) contains the definitions for `BROWSER_STACK_USERNAME` and `BROWSER_STACK_ACCESS_KEY` used in the GitHub Actions CI pipeline. When developing locally, you must provide your own credentials in order to run `npm run test-xbrowser`. You can register for an account for free on [the BrowserStack official website here](https://www.browserstack.com/).
+[/.github/workflows/javascript.yml](/.github/workflows/javascript.yml) contains the definitions for `BROWSERSTACK_USERNAME` and `BROWSERSTACK_ACCESS_KEY` used in the GitHub Actions CI pipeline. When developing locally, you must provide your own credentials in order to run `npm run test-browser-browserstack`. You can register for an account for free on [the BrowserStack official website here](https://www.browserstack.com/).
 
 ### Contributing