Fix insert&delete cases dead data.

[ColinLeeo]

In this PR:

1. remove useless write lock on schema cache when execute deletion
2. coordinator will acquire a read lock on schema cache, which will block deletion's cache invalidation.
3. solves the DEAD data problem: these data have no metadata but only data.

[ColinLeeo]

You can reproduce the problem using the steps below:
add code at the end of function validateSchema()

    try {
      Thread.sleep(10 * 1000);
    } catch (InterruptedException e) {
      // nothing
    }

run create and insert in one cli:

CREATE TIMESERIES root.db.d1.s1 WITH DATATYPE=INT32, ENCODING=PLAIN
INSERT INTO root.db.d1(timestamp,s1) values(1,1)

run delete on another cli:

delete timeseries  root.db.d1.s1

Without this patch, Insert operation will insert data into root.db.d1.s1 that has been deleted in another cli.
While with this patch, delete operation will wait insert operation finish so it can delete timeseries safely.