Remove non compiling APIs due to a dart-lang bug

[passsy]

Bug dart-lang/sdk#35518 prevents calls from external classes to those methods. the generic bound type is not correctly passed to the method resulting in a wrong inferred argument bounds violation.

Removed extensions:

• KIterable<T>.associateWithTo
• Kiterable<T>.filterTo
• KIterable<T>.filterIndexedTo
• KIterable<T>.filterNotTo
• KIterable<T>.filterNotNullTo
• KIterable<T>.groupByTo
• KMap<T>.mapKeysTo
• KMap<T>.mapValuesTo

Other ..To extensions like KIterable<T>.flatMapTo aren't affected. They don't have a generic type of the mixin in their generic type bounds.

[codecov]

Codecov Report

Merging #46 into master will decrease coverage by 0.19%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master      #46     +/-   ##
=========================================
- Coverage   94.19%   93.99%   -0.2%     
=========================================
  Files          25       25             
  Lines        1515     1515             
=========================================
- Hits         1427     1424      -3     
- Misses         88       91      +3

Impacted Files	Coverage Δ
lib/src/extension/map_extensions_mixin.dart	100% <ø> (ø)	⬆️
lib/src/extension/iterable_extension_mixin.dart	96.07% <ø> (-0.46%)	⬇️

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