slack-19.0: disable --config-file-not-found-handling on v15 tests, remove mysql57 CI

[timvaillancourt]

Description

This PR prevents the flag --config-file-not-found-handling to be set on upgrade/downgrade tests where binaries are not v19, using this tweak below. Also CI tests for mysql57 were deleted

vitess/examples/common/env.sh

Lines 35 to 38 in 1f8c487

	BINARY_VERSION=$($binary --version | grep -o "Version: 1[0-9]\.[0-9]*\.[0-9]*" | awk '{print $2}')
	if [[ "${BINARY_VERSION}" =~ 19.0.[0-9]* ]]; then
	alias $binary="$binary --config-file-not-found-handling=ignore"
	fi

This prevents the error unknown flag: --config-file-not-found-handling on some slack-15.0-downgrade CI

Failures in the following CI are expected and will be fixed in a subsequent PR:

• Query Serving (Queries) - Upgrade Downgrade Testing
• Query Serving (Schema) - Upgrade Downgrade Testing

Both of these CIs are currently not-required for merge

Related Issue(s)

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

Deployment Notes