[camera] Migrate maven repo from jcenter to mavenCentral

[jmagman]

The jcenter maven repository is being sunset and is currently readonly. Migrate to mavenCentral.

Remove exoplayer workaround introduced in #977. See also google/ExoPlayer#5246.
Remove trailing whitespace from CHANGELOG and pubspec.

camera part of flutter/flutter#82847

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide] and the [C++, Objective-C, Java style guides]. (Note that unlike the flutter/flutter repo, the flutter/plugins repo does use dart format. See plugin_tool format)
• I signed the [CLA].
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the [pub versioning philosophy].
• I updated CHANGELOG.md to add a description of the change.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test exempt.
• All existing and new tests are passing.

[mvanbeusekom]

I think the version number should be updated as a patch update. Since the Camera plugin is still in preview the version digits move one position to the left according to the Package versioning documentation.

[jmagman]

I think the version number should be updated as a patch update. Since the Camera plugin is still in preview the version digits move one position to the left according to the Package versioning documentation.

Thanks for the catch, done!

[mvanbeusekom]

LGTM

[fluttergithubbot]

This pull request is not suitable for automatic merging in its current state.

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