FLINK-37891: Remove SQL Server CDC documentation for initial-only

[morozov]

This documentation should have been updated as part of #1732.

See the actual code:

flink-cdc/flink-cdc-connect/flink-cdc-source-connectors/flink-connector-sqlserver-cdc/src/main/java/org/apache/flink/cdc/connectors/sqlserver/table/SqlServerTableFactory.java

Lines 236 to 242 in 0faf387

	throw new ValidationException(
	String.format(
	"Invalid value for option '%s'. Supported values are [%s, %s], but was: %s",
	SCAN_STARTUP_MODE.key(),
	SCAN_STARTUP_MODE_VALUE_INITIAL,
	SCAN_STARTUP_MODE_VALUE_LATEST,
	modeString));

[GOODBOY008]

@morozov Great catch. LGTM