remove legacy mode

[gabrielittner]

• remove useLegacyMode and delete the old configuration
• remove the groovy build configuration

Follow ups:

• simplify the maven-publish setup (like applying the plugin immediately instead of in afterEvaluate)
• I will create an issue to outline my general idea of where to go from here

[codecov]

Codecov Report

Merging #135 into master will increase coverage by 9.54%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #135      +/-   ##
============================================
+ Coverage     33.70%   43.25%   +9.54%     
  Complexity       52       52              
============================================
  Files            22       20       -2     
  Lines           448      363      -85     
  Branches         80       60      -20     
============================================
+ Hits            151      157       +6     
+ Misses          266      182      -84     
+ Partials         31       24       -7     

Impacted Files	Coverage Δ	Complexity Δ
...ktech/maven/publish/MavenPublishPluginExtension.kt	65.00% <ø> (-1.67%)	4.00 <0.00> (-1.00)
...com/vanniktech/maven/publish/MavenPublishPlugin.kt	63.63% <100.00%> (ø)	7.00 <1.00> (?)
...com/vanniktech/maven/publish/MavenPublishTarget.kt	90.00% <0.00%> (-10.00%)	7.00% <0.00%> (ø%)
...in/com/vanniktech/maven/publish/MavenPublishPom.kt	97.14% <0.00%> (-2.86%)	16.00% <0.00%> (-1.00%)
...vanniktech/maven/publish/MavenPublishConfigurer.kt	62.88% <0.00%> (+62.88%)	14.00% <0.00%> (+14.00%)

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[vanniktech]

Nice!