package/qt6/qt6base: remove -DFEATURE_concurrent=OFF from uncondtional options

Since commit
a39e0b95e1d927599e212098d1db4d2fafb2a35c ("package/qt6/qt6base: add
support for concurrent module"), we have an explicit option that
enables/disables concurrent support, so it no longer makes sense to
explicitly disable it unconditionnally first.

Signed-off-by: Hannah Kiekens <hannah.kiekens@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/qt6/qt6base/qt6base.mk

@@ -43,7 +43,6 @@ QT6BASE_INSTALL_STAGING = YES
 QT6BASE_CONF_OPTS = \
 	-DQT_HOST_PATH=$(HOST_DIR) \
 	-DINSTALL_ARCHDATADIR=lib/qt6 \
-	-DFEATURE_concurrent=OFF \
 	-DFEATURE_xml=OFF \
 	-DFEATURE_sql=OFF \
 	-DFEATURE_testlib=OFF \