build: Makes rcc output always deterministic

The Qt Resource Compiler (rcc) has a command-line option
`--format-version` which has the default value 2.

The only difference from `--format-version 1` is adding a last modified
timestamp to the output file. That, in turn, forces us to use
`QT_RCC_SOURCE_DATE_OVERRIDE=1` to get deterministic builds.

This change makes rcc output always deterministic by using
`--format-version 1` option that makes usage of the
`QT_RCC_SOURCE_DATE_OVERRIDE` needless. Also it improves interaction
with ccache.

Co-authored-by: fanquake <fanquake@gmail.com>

contrib/gitian-descriptors/gitian-linux.yml

@@ -56,7 +56,6 @@ script: |
   HOST_CXXFLAGS="-O2 -g"
   HOST_LDFLAGS_BASE="-static-libstdc++ -Wl,-O2"
 
-  export QT_RCC_SOURCE_DATE_OVERRIDE=1
   export TZ="UTC"
   export BUILD_DIR="$PWD"
   mkdir -p ${WRAP_DIR}

contrib/gitian-descriptors/gitian-osx.yml

@@ -42,7 +42,6 @@ script: |
   FAKETIME_HOST_PROGS=""
   FAKETIME_PROGS="ar ranlib date dmg xorrisofs"
 
-  export QT_RCC_SOURCE_DATE_OVERRIDE=1
   export TZ="UTC"
   export BUILD_DIR="$PWD"
   mkdir -p ${WRAP_DIR}

contrib/gitian-descriptors/gitian-win.yml

@@ -38,7 +38,6 @@ script: |
   HOST_CFLAGS="-O2 -g -fno-ident"
   HOST_CXXFLAGS="-O2 -g -fno-ident"
 
-  export QT_RCC_SOURCE_DATE_OVERRIDE=1
   export TZ="UTC"
   export BUILD_DIR="$PWD"
   mkdir -p ${WRAP_DIR}