Remove maxNames from top-level RA and CA configs

[aarongable]

This is a cleanup / followup to #7993

The max names per cert is now enforced at the per-profile level in the RA. The config change has been deployed (IN-11055) so we can remove the config item left behind:

boulder/cmd/boulder-ra/main.go

Lines 243 to 251 in 3250145

	// TODO(#7993): Remove this fallback and make ValidationProfile.MaxNames a
	// required config field. We don't do any validation on the value of this
	// top-level MaxNames because that happens inside the call to
	// NewValidationProfiles below.
	for _, pc := range c.RA.ValidationProfiles {
	if pc.MaxNames == 0 {
	pc.MaxNames = c.RA.MaxNames
	}
	}

If we like, we can also remove the configurable enforcement in the CA:

boulder/cmd/boulder-ca/main.go

Lines 71 to 76 in 3250145

	// MaxNames is the maximum number of subjectAltNames in a single cert.
	// The value supplied MUST be greater than 0 and no more than 100. These
	// limits are per section 7.1 of our combined CP/CPS, under "DV-SSL
	// Subscriber Certificate". The value must match the RA and WFE
	// configurations.
	MaxNames int `validate:"required,min=1,max=100"`

This could be replaced with a custom lint, as suggested by #5492

[arsenalzp]

Hello,
Is this issue suitable for project newcomers who whats to contribute and familiarize to it?

[aarongable]

Yes, that is why it has the "starter" label.

[arsenalzp]

Let me work on it.
Thank you!