audio: Fix for failure in CTS MediaRecorderTest cases

 -Issue: MediaRecorder CTS test cases are failing.

 -Running the CTS test "testRecorderRandomAction" at
  beginning sets the huge file size and StageFrightRecorder
  set the 64 bit file offset. In MPEG4 writer
  estimateMoovBoxSize depends on a static const variable
  which uses this file offset info. As the variable to
  calculate estimateMoovBoxSize is static const it remains
  same for next media recording session even if file size
  is small.

 -Fix: Don't use static const variable which is used to
  calculate estimateMoovBoxSize as its value may change
  depending on file offsets.

 CRS-Fixed: 629448

Change-Id: Icdb8658a69667663ba686ae51755f461dd35712c