Revert "Add 'ForceDebugInfo' -flag to linux desktop binaries"

Now debug symbols are added in qtlibs as well and library size
is huge. We need additional 'separate_debug_info' flag in
addition to this but currently there isn't support for it in
coin. That's why we need to revert this change until coin has
full support for this.

This reverts commit b0b6b05.

Change-Id: I7d36d2778433d2034420c209b73d21b5af32249f
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Iikka Eklund <iikka.eklund@qt.io>

coin/platform_configs/default.txt

@@ -12,7 +12,7 @@ qtci-linux-Ubuntu-16.04-x86_64-2                                    GCC
 qtci-linux-openSUSE-42.3-x86_64                                     GCC         DeveloperBuild NoPch
 qtci-linux-openSUSE-42.3-x86_64                                     ICC_18      DeveloperBuild NoPch DisableTests
 qtci-linux-RHEL-6.6-x86_64                                          GCC         Release ForceDebugInfo
-qtci-linux-RHEL-7.4-x86_64                                          GCC         Packaging Release NoUseGoldLinker ForceDebugInfo
+qtci-linux-RHEL-7.4-x86_64                                          GCC         Packaging Release NoUseGoldLinker
 qtci-macos-10.12-x86_64-8                                           Clang       Packaging DebugAndRelease Release
 qtci-osx-10.11-x86_64-3                                             Clang       DeveloperBuild Release QtNamespace NoPch
 qtci-osx-10.10-x86_64                                               Clang       Release NoFramework DisableTests