remove php7.3

tools/internal_ci/helper_scripts/prepare_build_macos_rc

@@ -190,16 +190,16 @@ then
   # It's required to update homebrew because it won't work with the default version Kokoro has.
   # This can be fragile though because the future version of brew can break - consider pinning
   # the formulas if that happens (see https://github.com/grpc/grpc/pull/24837).
-  brew update || true
+  #brew update || true
   # macos mojave support for php7.3 brew formula removed MacOS Mojave support here: https://github.com/Homebrew/homebrew-core/commit/d8496609d310a233bfb46272ec7948845f32d7c5#diff-df64282b6e4230b6f35468dfbbd500fcd62b0f93b01b2b161e92f512b7feb1a3
   # so we need earlier version of the formulata than that. See https://github.com/grpc/grpc/pull/24837 for an example of pinning homebrew formulas to a specific commit.
   #(cd /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core; git checkout 10b1944581fbbdc216057fd70e89dbbe3d04161e)
-  brew config
+  #brew config
 
-  brew install php@7.4 || true
-  export LDFLAGS="-L/usr/local/opt/php@7.4/lib ${LDFLAGS}"
-  export CPPFLAGS="-I/usr/local/opt/php@7.4/include ${CPPFLAGS}"
-  export PATH="/usr/local/opt/php@7.4/bin:/usr/local/opt/php@7.4/sbin:${PATH}"
+  #brew install php@7.4 || true
+  #export LDFLAGS="-L/usr/local/opt/php@7.4/lib ${LDFLAGS}"
+  #export CPPFLAGS="-I/usr/local/opt/php@7.4/include ${CPPFLAGS}"
+  #export PATH="/usr/local/opt/php@7.4/bin:/usr/local/opt/php@7.4/sbin:${PATH}"
 
   # the exit code from "brew install php@7.3" is useless
   # so instead we check if PHP was indeed installed successfully.