Fix cassandra delete edge with label covered too many lines

[Linary]

Change-Id: I8a4b000c7d91e542fbe30140b770062a0376082d

[codecov]

Codecov Report

Merging #727 into master will increase coverage by 0.01%.
The diff coverage is 90%.

@@             Coverage Diff              @@
##             master     #727      +/-   ##
============================================
+ Coverage     71.12%   71.13%   +0.01%     
  Complexity     4330     4330              
============================================
  Files           281      281              
  Lines         20693    20699       +6     
  Branches       2919     2920       +1     
============================================
+ Hits          14718    14725       +7     
+ Misses         4527     4524       -3     
- Partials       1448     1450       +2

Impacted Files	Coverage Δ	Complexity Δ
...graph/backend/store/cassandra/CassandraTables.java	87.14% <90%> (+0.22%)	1 <0> (ø)	⬇️
...a/com/baidu/hugegraph/backend/query/Condition.java	77.59% <0%> (-0.83%)	31% <0%> (ø)
...n/java/com/baidu/hugegraph/task/TaskScheduler.java	71.37% <0%> (+1.14%)	44% <0%> (ø)	⬇️

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