fix: remove fields empty check

[MichaelLeeHZ]

Which issue does this PR close?

Closes #

Rationale for this change

Sometime there is no fields in a table, error occurs when data writing :

java.lang.IllegalArgumentException: Empty.fields
        at io.shaded.ceresdb.common.util.Requires.requireTrue(Requires.java:72)
        at io.shaded.ceresdb.models.Point$PointBuilder.check(Point.java:84)
        at io.shaded.ceresdb.models.Point$PointBuilder.build(Point.java:78)

What changes are included in this PR?

Remove fields empty check.

Are there any user-facing changes?

How does this change test

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[mrrtree]

LGTM