qt: remove the BR2_PACKAGE_QT_JAVASCRIPTCORE option

The BR2_PACKAGE_QT_JAVASCRIPTCORE option was available to force the
activation or disabling of the JIT compiler in the Qt Javascript
interpreter. However, the JIT compiler is not available for all
architectures, so forcing its activation does not always
work. Moreover, Qt knows by itself for which architectures JIT support
is possible, and will automatically enable it if possible.

Therefore, this option was in fact useless, and causing build problems
when enabled on architectures for which the JIT support was not
available. This commit removes this option and there is no
replacement: Qt will enable JIT at compile time when possible.

Fixes:

  http://autobuild.buildroot.org/results/aae/aaeb82753b7654eeca679ded5d0211ceebda3ea2/build-end.log
  http://autobuild.buildroot.org/results/367/3670e4f03ff0ce114c90bd7139243d82c427b52a/build-end.log



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>