Change Requires-Dist format to not use parentheses

[uranusjr]

According to the Requires-Dist section in the active Core Metadata specification:

A version specifier. Tools parsing the format should accept optional parentheses around this, but tools generating it should not use parentheses.

wheel currently generates the version with parentheses, which is acceptable but not recommended. The format triggers bugs in the parsing tool (pypa/packaging#336). It would be perfectly reasonable to not change this due to backwards compatibility, but I want to raise the possibility since the paranthesis requirement has been removed for quite a while and may no longer be relevant.

[wimglenn]

This issue is outdated - there are no longer superfluous parens around the version specifier (fixed by 2a0a487). However, there are still superfluous parens on conditions, probably due to some code around here.