audio :Close HotWord audio source if it is already opened

- HotWord GTS test tries to record using second instance
  of HotWord Audio Source while one is already active.
  AudioPolicyManagerALSA is not closing the previous audio
  input before starting the second input.
- AudioHardwareALSA::openInputStream rejects opening
  of the second instance of audio input.
- HotWordAudioSource GTS test case fails due to above
  reasons.
- Fix is to enable the code that closes the previous
  input before starting the second audio input.
- Remove the code in openInputStream that is restricting
  the second record client. This is not needed now as it
  is already done in startInput of AudioPolicyManagerALSA

Change-Id: I63cd5061e23bef6c1f7c52cadd65833778e34018
CRs-Fixed: 591788