Drop explicit loop

[asvetlov]

Use asyncio.get_event_loop() instead if the loop instance is needed.
All aiohttp objects work with the currently running loop, a creation of aiohttp instances, e.g. ClientSession when the loop is not running is forbidden.

As a side effect of PR passing callables for aiohttp_server() and aiohttp_client pytest fixtures are forbidden, please call these callables explicitly.

[codecov-io]

Codecov Report

Merging #3580 into master will decrease coverage by 0.04%.
The diff coverage is 93.47%.

@@            Coverage Diff             @@
##           master    #3580      +/-   ##
==========================================
- Coverage   97.79%   97.74%   -0.05%     
==========================================
  Files          43       43              
  Lines        8653     8617      -36     
  Branches     1385     1378       -7     
==========================================
- Hits         8462     8423      -39     
- Misses         81       83       +2     
- Partials      110      111       +1

Impacted Files	Coverage Δ
aiohttp/web_runner.py	97.63% <ø> (-0.02%)	⬇️
aiohttp/abc.py	100% <ø> (ø)	⬆️
aiohttp/streams.py	97.92% <ø> (-0.52%)	⬇️
aiohttp/client_reqrep.py	97.01% <ø> (-0.01%)	⬇️
aiohttp/worker.py	97.5% <ø> (-0.05%)	⬇️
aiohttp/connector.py	97.24% <100%> (ø)	⬆️
aiohttp/helpers.py	97.48% <100%> (+0.02%)	⬆️
aiohttp/resolver.py	100% <100%> (ø)	⬆️
aiohttp/pytest_plugin.py	97.35% <100%> (-0.09%)	⬇️
aiohttp/web_protocol.py	91.74% <100%> (-0.03%)	⬇️
... and 6 more

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[lgtm-com]

This pull request introduces 6 alerts when merging b9d88ff into 6fa0be8 - view on LGTM.com

new alerts:

• 5 for Wrong name for an argument in a class instantiation
• 1 for Module is imported with 'import' and 'import from'

[lgtm-com]

This pull request fixes 1 alert when merging d12719b into 6fa0be8 - view on LGTM.com

fixed alerts:

• 1 for Module-level cyclic import

[lgtm-com]

This pull request fixes 1 alert when merging 50d306e into 6fa0be8 - view on LGTM.com

fixed alerts:

• 1 for Module-level cyclic import

[lgtm-com]

This pull request fixes 1 alert when merging 99e839d into 79364ce - view on LGTM.com

fixed alerts:

• 1 for Module-level cyclic import

[lgtm-com]

This pull request fixes 1 alert when merging c58a0e6 into e1eb27a - view on LGTM.com

fixed alerts:

• 1 for Module-level cyclic import