Remove the unused isStream property on various Streams

[Snuffleupagus]

This property was added all the way back in PR #542, but hasn't actually been relied upon ever since PR #692.
Note that there's a isStream() utility function which replaced the property years ago, hence the isStream property is now dead code.

[Snuffleupagus]

/botio test

[pdfjsbot]

From: Bot.io (Windows)

---

Received

Command cmd_test from @Snuffleupagus received. Current queue size: 0

Live output at: http://107.22.172.223:8877/375e949bd716e6a/output.txt

[pdfjsbot]

From: Bot.io (Linux)

---

Received

Command cmd_test from @Snuffleupagus received. Current queue size: 0

Live output at: http://107.21.233.14:8877/1feb30079001e83/output.txt

[pdfjsbot]

From: Bot.io (Linux)

---

Success

Full output at http://107.21.233.14:8877/1feb30079001e83/output.txt

Total script time: 25.37 mins

• Font tests: Passed
• Unit tests: Passed
• Regression tests: Passed

[pdfjsbot]

From: Bot.io (Windows)

---

Success

Full output at http://107.22.172.223:8877/375e949bd716e6a/output.txt

Total script time: 25.64 mins

• Font tests: Passed
• Unit tests: Passed
• Regression tests: Passed

[timvandermeij]

/botio-linux preview

[pdfjsbot]

From: Bot.io (Linux)

---

Received

Command cmd_preview from @timvandermeij received. Current queue size: 0

Live output at: http://107.21.233.14:8877/5cc7ad85df492d7/output.txt

[pdfjsbot]

From: Bot.io (Linux)

---

Success

Full output at http://107.21.233.14:8877/5cc7ad85df492d7/output.txt

Total script time: 2.28 mins

Published

• Viewer: http://107.21.233.14:8877/5cc7ad85df492d7/web/viewer.html
• Extension: http://107.21.233.14:8877/5cc7ad85df492d7/extensions/firefox/pdf.js.xpi

[timvandermeij]

Thank you for the cleanup!