package/pkg-cmake: <pkg>_SUBDIR cleanup

No functional change is brought by this modification.

This patch removes redundant <pkg>_SRCDIR declaration
  (already defined in pkg-generic.mk)

Signed-off-by: Lionel Orry <lionel.orry@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/pkg-cmake.mk

@@ -60,8 +60,6 @@ $(2)_INSTALL_OPTS		?= install
 $(2)_INSTALL_STAGING_OPTS	?= DESTDIR=$$(STAGING_DIR) install/fast
 $(2)_INSTALL_TARGET_OPTS		?= DESTDIR=$$(TARGET_DIR) install/fast
 
-$(2)_SRCDIR			= $$($(2)_DIR)/$$($(2)_SUBDIR)
-
 $(3)_SUPPORTS_IN_SOURCE_BUILD ?= YES