`stdout`/`stderr` history is always retained in memory

[TerrorJack]

Describe the bug
Since #737, all writes to stdout/stderr are forced to be retained in memory, because the console_history flag was forcibly turned on. This might be a minor source of memory leak.

To Reproduce
See above.

Expected behavior
When not compiling for ghc-testsuite, the stdout/stderr writes should propagate to the underlying flush function. Other than keeping a line-based cache in the browser case, the writes should not be cached.

Environment

• OS name + version: Docker dev image
• Version of the code: latest master revision

Additional context
Add any other context about the problem here.