[data]Remove use of browserstack.

[lina128]

This change is 

[nsthorat]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @dsmilkov, @lina128, and @nsthorat)

---

tfjs-data/package.json, line 25 at r1 (raw file):

    "jasmine-core": "~3.1.0",
    "karma": "~4.0.1",
    "karma-browserstack-launcher": "~1.4.0",

remove this

---

tfjs-data/package.json, line 54 at r1 (raw file):

    "test-ci": "ts-node src/test_node.ts",
    "test-snippets": "ts-node ./scripts/test_snippets.ts",
    "run-browserstack": "karma start --browsers='bs_firefox_mac,bs_chrome_mac' --singleRun",

remover this

[lina128]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @dsmilkov, @lina128, and @nsthorat)

tfjs-data/package.json, line 25 at r1 (raw file):

    "jasmine-core": "~3.1.0",
    "karma": "~4.0.1",
    "karma-browserstack-launcher": "~1.4.0",

remove this

tfjs-data/package.json, line 54 at r1 (raw file):

    "test-ci": "ts-node src/test_node.ts",
    "test-snippets": "ts-node ./scripts/test_snippets.ts",
    "run-browserstack": "karma start --browsers='bs_firefox_mac,bs_chrome_mac' --singleRun",

remover this

Done.

[dsmilkov]

Reviewed 2 of 3 files at r1, 2 of 2 files at r2.
Reviewable status: complete! 2 of 1 approvals obtained (waiting on @dsmilkov and @lina128)