Remove C++17 flags from g++ and clang

The flags are already being applied by QMAKE.

.travis.yml

@@ -12,7 +12,7 @@ matrix:
         - g++-7
     env:
     - QMAKE_SPEC=linux-g++
-    
+
   - os: linux
     env:
     - QMAKE_SPEC=linux-clang

advancedSettings.pro

@@ -36,6 +36,7 @@ TEMPLATE = app
 }
 
 win32-clang-msvc{
+    #clang-msvc does not enable the c++17 flag with qmake's c++1z flag.
     QMAKE_CXXFLAGS += /std:c++17
 }
 
@@ -43,7 +44,6 @@ win32-clang-msvc{
     #g++-7 is needed for C++17 features. travis does not supply this by default.
     QMAKE_CXX = g++-7
     QMAKE_CXXFLAGS += -Werror
-    QMAKE_CXXFLAGS += -std=c++17
 }
 
 #Look for anything clang that is not clang-msvc, since it does not
@@ -52,7 +52,6 @@ win32-clang-msvc{
     QMAKE_CXXFLAGS += -Werror
     #All includes from the third-party directory will not warn.
     QMAKE_CXXFLAGS += --system-header-prefix=third-party
-    QMAKE_CXXFLAGS += -std=c++17
 }
 SOURCES += src/main.cpp\
     src/overlaycontroller.cpp \