[ruby] Remove unnecessary and bug-creating code in platform.rb.

[ch-saeki]

Description

When calling selenium's cygwin? method from ruby on cygwin, regexp match results was returning different judgment result from the actual one, so it was removed.

Motivation and Context

I ran it from cygwin, but it didn't return the correct results, so I looked into it.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[CLAassistant]

All committers have signed the CLA.

[titusfortner]

Ah, yes, looks like successive rubocop updates broke this. Thanks.