fix: remove deprecated methods

[elharo]

This library is pre-1.0. If any dependencies need this, we should find out now so we can undeprecate these methods.

[codecov]

Codecov Report

Merging #537 (9f111fc) into master (f2ab4f1) will increase coverage by 0.05%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #537      +/-   ##
============================================
+ Coverage     79.87%   79.92%   +0.05%     
+ Complexity      424      421       -3     
============================================
  Files            28       28              
  Lines          1983     1978       -5     
  Branches        215      215              
============================================
- Hits           1584     1581       -3     
+ Misses          286      284       -2     
  Partials        113      113              

Impacted Files	Coverage Δ	Complexity Δ
...om/google/auth/appengine/AppEngineCredentials.java	72.91% <ø> (+1.21%)	13.00 <0.00> (-3.00)	⬆️

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[chingor13]

For context, I added these overrides because users were confused calling the static getApplicationDefault() on the AppEngineCredentials class. AppEngineCredentials didn't provide this method (it would fall back to use the superclass GoogleCredentials' implementaiton) so we added this deprecation warning to keep folks from using this as it will never return an instance of AppEngineCredentials.

[chingor13]

Need to remove the direct dependency declaration on google-http-client for the appengine artifact.