Remove old code for folder support in interpreter path settings

[karrtikr]

This check is done to ensure if entered interpreter path is valid, and if so, the path is returned. I don't see the point of these checks, as we shouldn't support entering interpreter paths this way.

Variable 'pythonPath' refers to the path user entered

vscode-python/src/client/common/configSettings.ts

Lines 674 to 696 in 620b614

	const KnownPythonExecutables = ['python', 'python4', 'python3.6', 'python3.5', 'python3', 'python2.7', 'python2'];
	for (let executableName of KnownPythonExecutables) {
	// Suffix with 'python' for linux and 'osx', and 'python.exe' for 'windows'.
	if (IS_WINDOWS) {
	executableName = `${executableName}.exe`;
	if (isValidPythonPath(path.join(pythonPath, executableName))) {
	return path.join(pythonPath, executableName);
	}
	if (isValidPythonPath(path.join(pythonPath, 'scripts', executableName))) {
	return path.join(pythonPath, 'scripts', executableName);
	}
	} else {
	if (isValidPythonPath(path.join(pythonPath, executableName))) {
	return path.join(pythonPath, executableName);
	}
	if (isValidPythonPath(path.join(pythonPath, 'bin', executableName))) {
	return path.join(pythonPath, 'bin', executableName);
	}
	}
	}
	return pythonPath;

Also, the first check when ensuring if interpreter path is valid is we should be checking if the entered path exists, which we're not doing.
This leads to us launching 14 exec commands <python> -c '1234' everytime a user enters an invalid path - leading to extension consuming too much CPU.

cc @DonJayamanne @karthiknadig

[DonJayamanne]

This was for portability.
Users wanted to set the python path in their settings for all users in a team across multiple os.
E.g. assume users have a relative path to a virtual env in their workspace .venv, that would work on Mac Linux and windows without any other change.

@brettcannon might recall this change bring added into the extension.

[karrtikr]

I see, @karthiknadig has observed that having these checks can wreck the SSH connection because of the 14 spawns made at worst case.
Also, I don't see this documented anywhere, wonder how many users are using this feature. Maybe we should add telemetry before deciding to removing these, or maybe have this as an optional feature?

[brettcannon]

Thanks to removing python.pythonPath, I don't think this is necessary anymore and we should just expect people to specify the full path to their environment's Python interpreter.

[gsinha18]

Picking it up

[karrtikr]

Checks have been converted to file exists check instead of launching the processes with #15725, so major concern with this issue is solved.

We should reconsider removing support for folders in python.defaultInterpreterPath setting: #15782. Add telemetry to see how many people use this: #12452 (comment).

[karrtikr]

Once #17821 is done asynchronously, validating these settings can also be conducted asynchronously, so support this scenario shouldn't be an issue.

[karrtikr]

We now have folder support inbuilt in the new discovery code, the old code is no longer needed.

[karrtikr]

Verification steps:

• Python: Select Interpreter -> Enter interpreter path -> Enter full path to the environment folder (for eg. full path to .venv folder, can even contain ~)
• Ensure interpreter still gets selected