feat: remove through2 dependency

[laljikanjareeya]

Towards #708

[codecov]

Codecov Report

Merging #770 into master will increase coverage by 0.27%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #770      +/-   ##
==========================================
+ Coverage   98.85%   99.13%   +0.27%     
==========================================
  Files          17       17              
  Lines       15769    15774       +5     
  Branches      952      951       -1     
==========================================
+ Hits        15589    15638      +49     
+ Misses        176      133      -43     
+ Partials        4        3       -1     

Impacted Files	Coverage Δ
src/table.ts	99.63% <100.00%> (+<0.01%)	⬆️
src/mutation.ts	100.00% <0.00%> (+0.23%)	⬆️
src/v2/bigtable_instance_admin_client.ts	98.78% <0.00%> (+0.65%)	⬆️
src/v2/bigtable_table_admin_client.ts	98.95% <0.00%> (+0.67%)	⬆️

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[laljikanjareeya]

@stephenplusplus Thanks for the review.

Two tests were failing:

1. invalid - duplicate row key
2. invalid - new row missing row key

I have also cross verify it with through2 version 4.0.2 these tests are also failing as they have removed destroy().
Based on that I just change the test cases.