Use ES to filter schools so that limit is correct

[mlt47]

Undo a temporary commit so that ElasticSearch does the filtering of closed schools meaning that the endpoint's limit query param works correctly.

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Pull Request Check List

• Unit Tests & Regression Tests Added (Optional)
• Removed Unnecessary Logs/System.Outs/Comments/TODOs
• Added enough Logging to monitor expected behaviour change
• Security - Injection - everything run by an interpreter (SQL, OS...) is either validated or escaped
• Security - Data Exposure - PII is not stored or sent unencrypted
• Security - Data Exposure - Test any altered or created endpoints using swagger
• Updated Release Procedure & Documentation (& Considered Implications to Previous Versions)
• Peer-Reviewed

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (0f2b386) 27.92% compared to head (eec5de3) 27.92%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #557   +/-   ##
=======================================
  Coverage   27.92%   27.92%           
=======================================
  Files         504      504           
  Lines       22954    22951    -3     
  Branches     2844     2843    -1     
=======================================
  Hits         6410     6410           
+ Misses      15932    15929    -3     
  Partials      612      612           

Files Changed	Coverage Δ
...ain/java/uk/ac/cam/cl/dtg/segue/api/Constants.java	81.18% <ø> (ø)
...cam/cl/dtg/segue/dao/schools/SchoolListReader.java	2.38% <0.00%> (+0.15%)	⬆️

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