improve "else" example

[Daniel-1276]

Affected document:
https://github.com/arduino/reference-en/blob/master/Language/Structure/Control%20Structure/else.adoc

Issue:
IMHO "&& temperature < 70" in condition2 is unnecessary.

Explanation:
condition1 is "true" if value is above "70". In this example all other "else" or "else if" conditions get ignored.
if value is below "70" first condition is "false" and second condition gets checked. This means already value is below 70 and must not be checked again.