Filter ABP CSS selectors

[yubiuser]

What does this PR aim to accomplish?:

Some ABP style lists contain lines with (extended) CSS selectors: ##, #$#, #?# and #@#

Currently our code strips all comments from the input file, converting e.g. good.com##bad-element to good.com leading to overblocking.
This PR deletes lines with CSS selectors before stripping comments.

Fixes #5246

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[yubiuser]

I also removed the sed that would remove lines containing / prior to paring. Such lines (e.g. whole URLs) should be marked as invalid which the are not when they were removed before parsing.

Fixed already