ABP holds onto multiple copies of the blocklist

[Swatinem]

So in `about:memory`, I have the following entries in notable strings:
```
│ │ │ ├──0.02 MB (00.00%) ++ string(length=8988, copies=1, "10NEWS.COM,37SIGNALS.COM,4KIDS.TV,6LYRICS.COM,7DAYSINABUDHABI.COM,7DAYSINDUBAI.COM" (truncated))
│ │ │ ├──0.02 MB (00.00%) ++ string(length=8988, copies=1, "10news.com,37signals.com,4kids.tv,6lyrics.com,7daysinabudhabi.com,7daysindubai.com" (truncated))
```
And a lot more, all duplicate uppercase and lowercase versions.

Strangely enough, only the lowercase version is again duplicated in a different zone/compartment.

Would be nice to clean this up so ABP is not a memory hog any more.

[p_hill]

If you still encounter this issue, you might want to post a more detailed description at https://issues.adblockplus.org