EC2: create_route() should allow overlapping CIDR's

[bblommers]

Fixes #6096

Partially reverts #5233

@mmerrill3 Do you remember the details about the linked PR that you raised? From my testing, overlapping CIDR's are allowed - as long as it's not a direct match.
The docs even mention this scenario, and explain what happens when overlapping routes exist: https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/ec2/client/create_route.html

Just wanted to know whether there was a specific reason that you added this check, maybe I missed some important details in my testing.

[codecov]

Codecov Report

Merging #6106 (0d23a58) into master (681db43) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #6106   +/-   ##
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  Coverage   96.24%   96.24%           
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  Files         766      766           
  Lines       75425    75425           
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  Hits        72594    72594           
  Misses       2831     2831           

Flag	Coverage Δ
servertests	36.94% <0.00%> (ø)
unittests	96.18% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
moto/ec2/models/route_tables.py	96.99% <100.00%> (ø)

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[mmerrill3]

@bblommers, it looks like my PR was too stringent in its check, given the documentation. There was no use case that I remember where overlapping routes were being disallowed, only that my thinking at the time was to treat route setups like adding CIDRs to a VPC.

[bblommers]

Thanks for confirming @mmerrill3 - so we'll just revert that part

[github-actions]

This is now part of moto >= 4.1.6.dev17