PubMatic: Remove req.ext.prebid from bid requests

[pm-viral-vala]

Hi Team,

The PubMatic Adapter is currently not utilizing the req.ext.prebid object from the backend. As this parameter is not being used, we can safely skip passing it in the PubMatic Adapter requests.

To address this, I am raising a PR to remove the req.ext.prebid parameter from PubMatic requests.

Let me know if you have any concerns or require further input.

[github-actions]

Code coverage summary

Note:

• Prebid team doesn't anticipate tests covering code paths that might result in marshal and unmarshal errors
• Coverage summary encompasses all commits leading up to the latest one, ba4567c

pubmatic

Refer here for heat map coverage report

github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:85:	MakeRequests				93.4%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:190:	validateAdSlot				91.3%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:233:	assignBannerSize			100.0%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:241:	assignBannerWidthAndHeight		100.0%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:249:	parseImpressionObject			91.7%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:340:	extractPubmaticExtFromRequest		96.6%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:391:	getAlternateBidderCodesFromRequestExt	100.0%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:409:	addKeywordsToExt			85.7%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:423:	MakeBids				90.7%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:505:	getNativeAdm				90.9%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:527:	getMapFromJSON				100.0%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:539:	populateFirstPartyDataImpAttributes	100.0%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:552:	populateAdUnitKey			100.0%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:567:	populateDctrKey				85.0%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:617:	getStringArray				100.0%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:630:	getBidType				100.0%
github.com/prebid/prebid-server/v3/adapters/pubmatic/pubmatic.go:650:	Builder					100.0%
total:									(statements)				93.1%