rtc: make rtc-lib explicitly non-modular

rtc: make rtc-lib explicitly non-modular

The Kconfig currently controlling compilation of this code is:

drivers/rtc/Kconfig:config RTC_LIB
drivers/rtc/Kconfig:    bool

...meaning that it currently is not being built as a module by anyone.

Lets remove the couple traces of modular infrastructure use, so that
when reading the driver there is no doubt it is builtin-only.

We delete the MODULE_LICENSE tag since all that information
is already contained at the top of the file in the comments.

We don't replace module.h with init.h since the file doesn't need that.
However we do add export.h since the file uses EXPORT_SYMBOL.

Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: rtc-linux@googlegroups.com
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>