Qbs: Remove useless DEFINES from .pro file

Change-Id: Iaa79e316bf1ffcf2370689db9d1fdd3836dbfe4d
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/qbsprojectmanager/qbsprojectmanager.pro

@@ -10,8 +10,6 @@ macx:QMAKE_LFLAGS += -Wl,-rpath,@loader_path/../
 
 QBS_BUILD_DIR_FWD_SLASHES = $$replace(QBS_BUILD_DIR, \\\\, /)
 DEFINES += QBS_BUILD_DIR=\\\"$$QBS_BUILD_DIR_FWD_SLASHES\\\"
-DEFINES += \
-    QBSPROJECTMANAGER_LIBRARY
 
 HEADERS = \
     qbsbuildconfiguration.h \