[windows] remove pip2 declaration to reduce pip version confusion

[derekwbrown]

What does this PR do?

removes the pip2 definition dependency, so that we don't have multiple pip installs

[ofek]

Let's instead change

datadog-agent/omnibus/config/software/datadog-agent-integrations-py2.rb

Lines 91 to 92 in 9bb9158

	pip = "#{windows_safe_path(python_2_embedded)}\\Scripts\\pip.exe"
	python = "#{windows_safe_path(python_2_embedded)}\\python.exe"

to

    python = "#{windows_safe_path(python_2_embedded)}\\python.exe"
    pip = "#{python} -m pip"

[olivielpeau]

On Windows, is it required (or more generally, what are the reasons) to ship pip with python directly, instead of installing it separately from python?

Asking because installing it separately is what's done on Linux/macOS and makes things more flexible, as it makes it easy to upgrade pip (which is quite frequent) separately from python upgrades (which are less frequent).

[derekwbrown]

After 6.13, we will repackage python such that it no longer includes pip itself. Then the installed pip will become the correct, only version

[derekwbrown]

Superseded by #3924