Summary:
This diff remove the assertion check from `getPgBackendPid` api used in java test suite to find out the pid of the backend process.
The definition of `getBackendPid` for connection manager has been introduced in this [[ https://phorge.dev.yugabyte.com/D41112 | D41112 ]]. It adds a assert check with connection manager, the test must run in `ConnectionManagerWarmupMode.NONE` mode in order to get the same PID most of the time. But it's not important for test to run in NONE mode, it completely depends on the test.
Therefore removing the assert check in this diff.

Test Plan:
Jenkins: enable connection manager, all tests

Make sure below tests definitely runs successfully with connection manager:

  # org.yb.pgsql.TestPgBackendMemoryContext#testLogBackendMemoryTexts
  # org.yb.pgsql.TestPgForeignKey#testForeignKeyConflictsWithSnapshotIsolation
  # org.yb.pgsql.TestPgForeignKey#testForeignKeyConflictsWithSerializableIsolation
  # org.yb.pgsql.TestPgSelect#testDistinctWithMultipleTypes

Reviewers: rbarigidad, devansh.saxena, skumar

Reviewed By: rbarigidad, devansh.saxena

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D42380