remove build timeout as perf bump (dotnet#4811)

* remove build timeout as perf bump, also try use hosted agent pool for netcore3.0 as well

* change back test agent pool

Author: frank-dong-ms-zz

build/ci/job-template.yml

@@ -53,7 +53,6 @@ jobs:
         displayName: Set LD_LIBRARY_PATH for Ubuntu to locate Native shared library in current running path
     - script: ${{ parameters.buildScript }} -$(_configuration) -buildArch=${{ parameters.architecture }}
       displayName: Build
-      timeoutInMinutes: 20
     - ${{ if eq(parameters.nightlyBuild, 'true') }}:
       - script: $(dotnetPath) restore $(nightlyBuildProjPath)
         displayName: Restore nightly build project