Remove deprecated `skip_equivalent` pyproj arg

Closes https://github.com/gjoseph92/stackstac/issues/173

Caused by https://github.com/pyproj4/pyproj/pull/1077.

FYI @snowman2 since https://github.com/pyproj4/pyproj/pull/824 used a DeprecationWarning, not a FutureWarning, the warning would not have typically been displayed to users. That's probably why neither I nor anybody else noticed it.

https://docs.python.org/3/library/warnings.html#warning-categories Class Description

DeprecationWarning Base category for warnings about deprecated features when those warnings are intended for other Python developers (ignored by default, unless triggered by code in main).

FutureWarning Base category for warnings about deprecated features when those warnings are intended for end users of applications that are written in Python.

gjoseph92 / stackstac

Remove deprecated `skip_equivalent` pyproj arg #174

https://docs.python.org/3/library/warnings.html#warning-categories Class	Description
DeprecationWarning	Base category for warnings about deprecated features when those warnings are intended for other Python developers (ignored by default, unless triggered by code in main).
FutureWarning	Base category for warnings about deprecated features when those warnings are intended for end users of applications that are written in Python.