fix: drop the pitSegments override, which no longer overrides anything

[marevol]

main does not compile since #208:

FesenClient.java:[40,67] cannot find symbol
  symbol:   class PitSegmentsRequest
  location: package org.codelibs.fesen.opensearch.action.admin.indices.segments
FesenClient.java:[826,5] method does not override or implement a method from a supertype

What went wrong

#208 rewrote every org.opensearch.* reference to org.codelibs.fesen.opensearch.*.
That rename was applied uniformly, but not every type survived the fork.
PitSegmentsRequest is one that did not, and fesen-httpclient's Client no longer
declares pitSegments, so FesenClient.pitSegments(...) overrides nothing and its
import resolves to nothing.

#208's CI could not have caught it. It was red from the day it opened because the
forked fesen-httpclient was not published yet, so fess-crawler-opensearch never
reached javac there. Merging it was what first compiled the module.

Fix

The override is removed, along with the two imports it needed
(IndicesSegmentResponse became unused with it). Nothing else referenced either.

The rest of the module was checked the same way

Every org.codelibs.fesen.opensearch.* name in fess-crawler-opensearch was
matched against the 2,491 classes in the published fesen-httpclient-3.8.1-SNAPSHOT
jar. PitSegmentsRequest was the only one missing — the one other flagged name,
XContentFactory.jsonBuilder, is a static import of a member and its class is
present.

Verification

• mvn clean package — BUILD SUCCESS (was a compilation failure on main).
• mvn clean install -DskipTests — BUILD SUCCESS.
• mvn test -pl fess-crawler-opensearch — 53 tests, 0 failures, FesenClientTest 12 of them.