breaking: remove legacy/build.gradle from template

[brodycj]

Platforms affected

Android

Motivation and Context

While looking into Gradle files to be updated & tested in PR #988, I discovered bin/templates/project/legacy/build.gradle which seems to be outdated and no longer needed.

Description

remove bin/templates/project/legacy/build.gradle

Testing

• tested this update with the spec test app in cordova-sqlite-storage

Checklist

• I've run the tests to see all new and existing tests pass - verified green CI build
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[codecov-commenter]

Codecov Report

Merging #989 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #989   +/-   ##
=======================================
  Coverage   68.11%   68.11%           
=======================================
  Files          21       21           
  Lines        1866     1866           
=======================================
  Hits         1271     1271           
  Misses        595      595           

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