Utilities/Release: Drop source archive generation in scripts

We will generate the `.tar.gz` and `.zip` source archives using
`git archive` in the scripts that drive the Linux build with Docker.

Utilities/Release/linux64_release.cmake

@@ -3,6 +3,7 @@ set(BOOTSTRAP_ARGS "--docdir=doc/cmake")
 set(HOST linux64)
 set(MAKE_PROGRAM "make")
 set(CPACK_BINARY_GENERATORS "STGZ TGZ")
+set(CPACK_SOURCE_GENERATORS "")
 set(CC /opt/gcc-8.2.0/bin/gcc)
 set(CXX /opt/gcc-8.2.0/bin/g++)
 set(CFLAGS   "")

Utilities/Release/osx_release.cmake

@@ -5,7 +5,7 @@ set(HOST dragnipur)
 set(MAKE_PROGRAM "make")
 set(MAKE "${MAKE_PROGRAM} -j5")
 set(CPACK_BINARY_GENERATORS "DragNDrop TGZ")
-set(CPACK_SOURCE_GENERATORS "TGZ TZ")
+set(CPACK_SOURCE_GENERATORS "")
 set(CPACK_DMG_FORMAT "UDBZ") #build using bzip2 for smaller package size
 set(CC clang)
 set(CXX clang++)

Utilities/Release/win32_release.cmake

@@ -5,7 +5,7 @@ set(PROCESSORS 16)
 set(HOST win32)
 set(RUN_LAUNCHER ~/rel/run)
 set(CPACK_BINARY_GENERATORS "WIX ZIP")
-set(CPACK_SOURCE_GENERATORS "ZIP")
+set(CPACK_SOURCE_GENERATORS "")
 set(MAKE_PROGRAM "ninja")
 set(MAKE "${MAKE_PROGRAM} -j16")
 set(qt_prefix "c:/Qt/5.12.1/msvc2017-32-w7-mt")