Revert 5c1cc4a40d84 in order to allow dashes in plugin directory names

[borysiasty]

A few weeks ago I pushed the 5c1cc4a commit, so QGIS started interpreting dashes in zip file names as a version suffix delimiter (e.g. MyPlugin-0.0.1.zip should contain "MyPlugin" directory). The purpose was to end a frequent confusion: plugin authors was naming zip files like that and they were reporting those zips are not installable.

However, now it turned out (see #32968) that dashes are also used in the directory names for some time (40 plugins for QGIS 3.x vs zero for 2.x), they are even officially allowed: https://docs.qgis.org/3.4/en/docs/pyqgis_developer_cookbook/plugins/releasing.html#validation . And yes, QGIS is able to import packages with dashes in names.

In this situation I guess we have to revert that commit (although personally I'm obviously against playing with fire and allowing dashes in Python packages).

Checklist

• Commit messages are descriptive and explain the rationale for changes
• Commits which fix bugs include Fixes #11111 at the bottom of the commit message
• I have read the QGIS Coding Standards and this PR complies with them
• New unit tests have been added for core changes
• I have run the scripts/prepare-commit.sh script before each commit
• I have evaluated whether it is appropriate for this PR to be backported, backport requests are left as label or comment