Remove unused katib-manager-rest

[hougangliu]

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1. Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

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This change is 

[johnugeorge]

I think, this will be useful to use rest calls for our DB interface. Mostly for debugging I guess, WHYT?

[hougangliu]

for now, only metrics related operations (create/delete/get) are available. I think the rest service is of little value now.

[gaocegege]

SGTM

/lgtm

[hougangliu]

@johnugeorge
katib-manager-rest is introduced in v1alpha1 when katib-manager works as a core role by which controller persists studyjob info into db and call it to get suggestion result, 3rd-party can call it to check StudyJob information (katib UI), suggestion service to call it to check trial result or else. by katib-manager-rest, 3rd-party can get studyjob info in REST way.
now, katib-manager just plays an internal DB interface role to persist only metrics and 3rd-party doesn't need it. so katib-manager-rest can say goodbye now.
WDYT?

[johnugeorge]

Sounds good. Just thinking if it is late to add to 0.7 release?

[hougangliu]

Sounds good. Just thinking if it is late to add to 0.7 release?

The risk is little since the change doesn't change katib-manger, katib-controller and suggestion algorithm code.

[johnugeorge]

/lgtm
/approve

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[hougangliu]

/test kubeflow-katib-presubmit