Revert subsegment synchronization changes

[willarmiros]

Issue #, if available:
#303

Description of changes:
This PR reverts the changes to the segment/subsegment synchronization logic made in the following previous PRs:

#250
#278
#279
#306

This should revert the SDK's synchronization behavior to a known good state in v2.8.0 and resolve the deadlocking issues. We maintained the public methods introduced by these PRs for backwards compatibility.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Merging #350 (cca3300) into master (d097192) will decrease coverage by 0.58%.
The diff coverage is 78.83%.

@@             Coverage Diff              @@
##             master     #350      +/-   ##
============================================
- Coverage     58.82%   58.24%   -0.59%     
- Complexity     1207     1210       +3     
============================================
  Files           131      131              
  Lines          5076     4948     -128     
  Branches        594      590       -4     
============================================
- Hits           2986     2882     -104     
+ Misses         1817     1791      -26     
- Partials        273      275       +2     

Impacted Files	Coverage Δ
.../main/java/com/amazonaws/xray/entities/Entity.java	100.00% <ø> (ø)
...ava/com/amazonaws/xray/entities/FacadeSegment.java	16.66% <ø> (ø)
...n/java/com/amazonaws/xray/emitters/UDPEmitter.java	42.85% <16.66%> (+19.45%)	⬆️
...va/com/amazonaws/xray/entities/SubsegmentImpl.java	69.81% <66.66%> (-2.02%)	⬇️
...zonaws/xray/strategy/DefaultStreamingStrategy.java	87.50% <72.72%> (-8.80%)	⬇️
...n/java/com/amazonaws/xray/entities/EntityImpl.java	85.58% <84.02%> (-1.47%)	⬇️
.../java/com/amazonaws/xray/entities/SegmentImpl.java	91.07% <94.28%> (-0.07%)	⬇️
...va/com/amazonaws/xray/entities/NoOpSubSegment.java	92.68% <0.00%> (-1.22%)	⬇️
.../java/com/amazonaws/xray/entities/NoOpSegment.java	96.42% <0.00%> (-1.20%)	⬇️
... and 4 more

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[wangzlei]

LGTM!