Remove default sensor_types, convert tabs to spaces

[AndrewEllis93]

• Remove default sensor_type: values to ensure that users are verifying their thermistors. Many users are just using the default values without actually checking.
• Add comments linking to Klipper thermistor list (so always up-to-date)
• Remove thermistor list at bottom of config files (if it exists - better to use the always up-to-date Klipper link)
• Hint at using "Generic 3950" for NTC 100k 3950, and also for Keenovo heaters
• Remove custom 3950 definition (if exists) - no longer necessary, Klipper thermistor accuracy bug has been fixed, and any new builders will be pulling a new version of Klipper.

[AndrewEllis93]

• Converted all tabs to white spaces, preserving alignment, so it displays correctly in all editors and on GitHub
• Commented out sensor_types - this makes the error easier to understand (thanks for the idea Tetsunosuke)

[AndrewEllis93]

Ensured newlines at the end of each file. Removed 3950 footnotes (if any)

[AndrewEllis93]

Side note: these EOF newlines don't seem to always display correctly in GitHub. When I download the raw files (not just view raw in browser), though, they are there.