Remove net461 from jaeger zipkin and otlp exporters

[cijothomas]

Towards #3190

[codecov]

Codecov Report

Merging #3194 (bc68a1b) into main (733c59a) will increase coverage by 0.22%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #3194      +/-   ##
==========================================
+ Coverage   84.91%   85.14%   +0.22%     
==========================================
  Files         259      259              
  Lines        9330     9330              
==========================================
+ Hits         7923     7944      +21     
+ Misses       1407     1386      -21     

Impacted Files	Coverage Δ
...ZPages/Implementation/ZPagesExporterEventSource.cs	56.25% <0.00%> (-6.25%)	⬇️
...heus/Implementation/PrometheusCollectionManager.cs	79.74% <0.00%> (-2.54%)	⬇️
...metryProtocol/Implementation/ActivityExtensions.cs	91.44% <0.00%> (+2.70%)	⬆️
...emetry.Api/Internal/OpenTelemetryApiEventSource.cs	82.35% <0.00%> (+2.94%)	⬆️
...tation/OpenTelemetryProtocolExporterEventSource.cs	85.00% <0.00%> (+10.00%)	⬆️
...xporter.OpenTelemetryProtocol/OtlpTraceExporter.cs	77.27% <0.00%> (+40.90%)	⬆️
...entation/ExportClient/OtlpGrpcTraceExportClient.cs	78.57% <0.00%> (+42.85%)	⬆️