Make the FT/Metrics 2.0 feature ready for release

[Azquelt]

• Remove the guard feature
• Mark the FT/Metrics 2.0 as GA/core
• Remove references to the guard feature from tests

Fixes #8886

[LibbyBot]

Code analysis and actions

DO NOT DELETE THIS COMMENT.

• 3 product code files were changed.

• Please describe in a separate comment how you tested your changes.

• 5 FAT files were changed, added, or removed.

• Check that the build did not break the affected FAT suite(s).

• 1 NLS files were changed and need an ID review.

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• dev/com.ibm.websphere.appserver.features/visibility/public/mpFT-Metrics-2.0-guard/resources/l10n/com.ibm.websphere.appserver.mpFT-Metrics-2.0-guard.properties

[Azquelt]

#build

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Please code review feature-related files, @OpenLiberty/delivery-approvers

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The build Azquelt-8935-20190912-1701
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[Azquelt]

Failures in the build do not appear to be related to this change.