Delete discovery gateway

[systay]

Description

This pull request removes the DiscoveryGateway struct and related files. The DiscoveryGateway has been our legacy gateway since the implementation of the new tabletgateway through #6155.

Related Issue(s)

• Contributes to Task: delete deprecated discoverygateway and legacy healthcheck code #9218

Checklist

• Should this PR be backported? NO
• Tests were added or are not required
• Documentation was added or is not required

[harshit-gangal]

the problem seems to be related to hostname, if you change the hostname from e0- to random the test starts working.
The bug may be a test thing when the hostname is the same.

[deepthi]

ah good point. we should change e0- to -20 to match the shard name and make it unique.

[deepthi]

-20 also conflicts. I guess we should make it 0.
I tried that, the next error is

--- FAIL: TestExecutorMaxPayloadSizeExceeded (0.00s)
    executor_test.go:1992:
        	Error Trace:	executor_test.go:1992
        	Error:      	Not equal:
        	            	expected: <nil>(<nil>)
        	            	actual  : *vterrors.fundamental(Code: NOT_FOUND
        	            	tablet aa-0000000010 not found
        	            	)
        	Test:       	TestExecutorMaxPayloadSizeExceeded
        	Messages:   	err should be nil

[harshit-gangal]

for failing test, the issue is due to a global session named primarySession getting used.
instead create a local session for those tests and use exec or executorExecSession instead of executorExec

[deepthi]

What I did instead is to not initialize primarySession when it is declared, but create it in each of the test env functions - createExecutorEnv etc. That seems to fix all the failures in this particular test.

[systay]

let's re-open when we have time to spend on it

[frouioui]

I will open a follow-up pull request rebased on top of this one to remove the Gateway interface introduced by #5992.

[systay]

I opened this PR, so I can't accept it, but it LGTM ⭐

Removing old code is the best ❤️

[frouioui]

@deepthi in healthcheck.go you left a ToDo to deprecate some variables. I am not sure which ones you were talking about. Can you guide me?

Link to the corresponding ToDo:
https://cs.github.com/vitessio/vitess/blob/605beab9015ce69840f014cabd98a8ecae4d9b31/go/vt/discovery/healthcheck.go#L70

[deepthi]

@deepthi in healthcheck.go you left a ToDo to deprecate some variables. I am not sure which ones you were talking about. Can you guide me?

Link to the corresponding ToDo: https://cs.github.com/vitessio/vitess/blob/605beab9015ce69840f014cabd98a8ecae4d9b31/go/vt/discovery/healthcheck.go#L70

Not deprecate, just change from exported -> not. All 6 flags below that comment should be reviewed to see if they are still being used outside discovery package. If not, we can change them back.