Installer: Do not create "Git Bash.lnk" in the app directory anymore

As of eec84b0 the shortcut from which the console window icon and title
are set is created dynamically by "Git Bash.vbs" in the temp directory.

Leave the code to delete "Git Bash.lnk" on uninstall in there to properly
clean-up a previous installation.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
Installer: Fix "an" -> "and" typo in code comments

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
Installer: Move DeleteFromVirtualStore to helpers.inc.iss

As it is more or less a generic helper function.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
Installer: Improve code comments

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
Installer: Reduce code duplication by refactoring into functions

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
Installer: Minor equalization of formatting

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>