revert: adds samples for CMEK

[olavloite]

See #1043

Temporarily reverts the addition of these samples, as encryption is not yet available in the Spanner client that is included in the BOM. Encryption requires Spanner client library version 6.x. The current BOM version is 5.1.0.

Reverts #989

[thiagotnunes]

Hum that is a good catch, but we can not revert these, otherwise the documentation will break.

[codecov]

Codecov Report

Merging #1044 (473bc12) into master (3b44e55) will increase coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #1044      +/-   ##
============================================
+ Coverage     85.22%   85.26%   +0.03%     
- Complexity     2657     2661       +4     
============================================
  Files           155      155              
  Lines         14453    14453              
  Branches       1362     1362              
============================================
+ Hits          12318    12323       +5     
+ Misses         1566     1562       -4     
+ Partials        569      568       -1     

Impacted Files	Coverage Δ	Complexity Δ
...a/com/google/cloud/spanner/SessionPoolOptions.java	69.53% <0.00%> (ø)	18.00% <0.00%> (+1.00%)
...cloud/spanner/connection/ReadWriteTransaction.java	82.38% <0.00%> (+0.27%)	60.00% <0.00%> (+1.00%)
...ain/java/com/google/cloud/spanner/SessionPool.java	89.12% <0.00%> (+0.38%)	73.00% <0.00%> (+2.00%)

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[thiagotnunes]

We updated the bom version now: dcfe398. This PR should be unnecessary.