"practices that tend to lock in"
Tend to? Erm, very vague there, should they tend to investigate?
Specifically, what the EU should do is remove the clause in Google's adsense that bans other adverts from other adnetworks that might 'confuse' the visitor to the site. It excludes competitors. They have no trademark control on that ad-block and hence no good reason to block competitors having similar blocks of pay per click adverts.
If Google's adblock is so distinctive, then why do they put the word 'Google' at the bottom? Exactly.
Secondly investigate the payout % to ensure they don't downgrade sites that have competitor adverts on them. If there is any evidence that they do, then force disclosure of the gross and net revenues for a each site they serve ads to (only needs to be disclosed to the site itself).
(Google say they pay out the 'majority' of revenue to advertisers, but the big guys have 90%+ cuts, so it follows that the little sites get very little, perhaps 10-15% to bring the average to 50.01%)
Fix their revenue and the rest will take care of itself, since it all hangs off their ability to fund unprofitable work with ad revenue and ultimately that ad revenue is taken out of the content providers money.
As for their search engine, their ability to maximize the revenue by tweaking the results is far less if sites also carry competitor adverts. And the more suboptimal the result will have to be to show the sites that only carry their ads.