chore!: Remove podspec support from framework tag

[dpogue]

Closes #812.

Platforms affected

iOS

Motivation and Context

<framework type="podspec"> has been deprecated in favour of the <podspec> tag that allows much more control over pod dependencies.

Description

Remove support for <framework type="podspec"> and print an error if such framework tags are found.

Testing

Removed unit tests around special case handling for podspec framework tags.

Checklist

• I've run the tests to see all new and existing tests pass
• 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)

[codecov-commenter]

Codecov Report

Merging #1340 (7445c88) into master (98910de) will decrease coverage by 0.04%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #1340      +/-   ##
==========================================
- Coverage   78.62%   78.58%   -0.04%     
==========================================
  Files          15       15              
  Lines        1801     1770      -31     
==========================================
- Hits         1416     1391      -25     
+ Misses        385      379       -6     

Impacted Files	Coverage Δ
lib/plugman/pluginHandlers.js	89.69% <0.00%> (-0.47%)	⬇️
lib/Api.js	71.11% <100.00%> (-0.88%)	⬇️

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[erisu]

Since this is a major release, I think it is safe to remove the deprecated framework tag's attribute podspec.

The new method <podspec> was introduced in Cordova-iOS@5.0.0 (Feb 07, 2019).

Plugin developers had 4 years to migrate to the new tag.