Delete proguard

[tobiasKaminsky]

As discussed in nextcloud/android-library#160 proguard.cfg is not correctly working.
As we do not use it, this should be removed.

[nextcloud-android-bot]

Lint

Type	Master	PR
Warnings	94	94
Errors

FindBugs (new)

Warning Type	Number
Bad practice Warnings	35
Correctness Warnings	164
Experimental Warnings	4
Internationalization Warnings	13
Malicious code vulnerability Warnings	9
Multithreaded correctness Warnings	9
Performance Warnings	125
Security Warnings	200
Dodgy code Warnings	135
Total	694

FindBugs (master)

Warning Type	Number
Bad practice Warnings	35
Correctness Warnings	164
Experimental Warnings	4
Internationalization Warnings	13
Malicious code vulnerability Warnings	9
Multithreaded correctness Warnings	9
Performance Warnings	125
Security Warnings	200
Dodgy code Warnings	135
Total	694

[codecov]

Codecov Report

Merging #3028 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #3028      +/-   ##
=========================================
+ Coverage     6.5%   6.51%   +<.01%     
=========================================
  Files         306     306              
  Lines       29986   29986              
  Branches     4311    4311              
=========================================
+ Hits         1952    1953       +1     
+ Misses      27742   27741       -1     
  Partials      292     292

Impacted Files	Coverage Δ
.../third_parties/daveKoeller/AlphanumComparator.java	83.33% <0%> (+1.19%)	⬆️

[AndyScherzinger]

👍