DOC: Remove CMake comments mentioning CMake 3.4
DOC: Remove CMake comments mentioning CMake 3.4

Remove comments mentioning CMake 3.4 since CMake minimum required
version is 3.9.5 which is greater than 3.4.

Change-Id: I2213a63ee0d8fd60961bbdf32cc26b3ffe543794

spinicist/ITK,BRAINSia/ITK,malaterre/ITK,fbudin69500/ITK,malaterre/ITK,spinicist/ITK,spinicist/ITK,richardbeare/ITK,richardbeare/ITK,fbudin69500/ITK,malaterre/ITK,Kitware/ITK,thewtex/ITK,fbudin69500/ITK,InsightSoftwareConsortium/ITK,richardbeare/ITK,fbudin69500/ITK,Kitware/ITK,blowekamp/ITK,Kitware/ITK,thewtex/ITK,hjmjohnson/ITK,thewtex/ITK,InsightSoftwareConsortium/ITK,spinicist/ITK,hjmjohnson/ITK,InsightSoftwareConsortium/ITK,LucasGandel/ITK,blowekamp/ITK,stnava/ITK,InsightSoftwareConsortium/ITK,LucasGandel/ITK,spinicist/ITK,vfonov/ITK,stnava/ITK,blowekamp/ITK,stnava/ITK,blowekamp/ITK,richardbeare/ITK,thewtex/ITK,InsightSoftwareConsortium/ITK,stnava/ITK,vfonov/ITK,malaterre/ITK,richardbeare/ITK,LucasGandel/ITK,LucasGandel/ITK,BRAINSia/ITK,hjmjohnson/ITK,hjmjohnson/ITK,LucasGandel/ITK,malaterre/ITK,Kitware/ITK,malaterre/ITK,InsightSoftwareConsortium/ITK,spinicist/ITK,BRAINSia/ITK,InsightSoftwareConsortium/ITK,thewtex/ITK,Kitware/ITK,stnava/ITK,stnava/ITK,hjmjohnson/ITK,thewtex/ITK,stnava/ITK,Kitware/ITK,hjmjohnson/ITK,BRAINSia/ITK,blowekamp/ITK,fbudin69500/ITK,fbudin69500/ITK,blowekamp/ITK,BRAINSia/ITK,stnava/ITK,vfonov/ITK,hjmjohnson/ITK,vfonov/ITK,vfonov/ITK,vfonov/ITK,spinicist/ITK,malaterre/ITK,blowekamp/ITK,malaterre/ITK,vfonov/ITK,LucasGandel/ITK,spinicist/ITK,LucasGandel/ITK,malaterre/ITK,LucasGandel/ITK,stnava/ITK,blowekamp/ITK,spinicist/ITK,thewtex/ITK,fbudin69500/ITK,richardbeare/ITK,vfonov/ITK,vfonov/ITK,fbudin69500/ITK,BRAINSia/ITK,richardbeare/ITK,Kitware/ITK,BRAINSia/ITK