floss: removing googletest manual build steps

* googletest packages (libgtest-dev and libgmock-dev) have pkg-config
  files now. So, the build and installation steps are no longer
  required.

* Here are the installation information about these packages:
  $ $ apt list --installed libgtest-dev libgmock-dev
  Listing... Done
  libgmock-dev/glinux-rodete-base-20220316.03.07,now 1.11.0-3 amd64
  [installed]
  libgtest-dev/glinux-rodete-base-20220316.03.07,now 1.11.0-3 amd64
  [installed]

  $dpkg -L libgtest-dev | grep gtest.pc
  /usr/lib/x86_64-linux-gnu/pkgconfig/gtest.pc

  $ dpkg -L libgmock-dev | grep gmock.pc
  /usr/lib/x86_64-linux-gnu/pkgconfig/gmock.pc

* Adding libabsl-dev package as it's required by libchrome.

Bug: 227287284
Tag: #floss
Test: ./biuld.py --target docs and ./build.py
Change-Id: I46c9f16ce328041c8953c5ad2b513719997fb096

README.md

@@ -30,7 +30,8 @@ sudo apt-get install repo git-core gnupg flex bison gperf build-essential \
   libprotobuf-dev ninja-build generate-ninja protobuf-compiler \
   libre2-9 debmake \
   llvm libc++abi-dev \
-  libre2-dev libdouble-conversion-dev
+  libre2-dev libdouble-conversion-dev \
+  libgtest-dev libgmock-dev libabsl-dev
 ```
 
 You will also need a recent-ish version of Rust and Cargo. Please follow the
@@ -89,26 +90,6 @@ popd
 sudo dpkg -i outdir/libchrome/*.deb
 ```
 
-The googletest packages provided by Debian/Ubuntu (libgmock-dev and
-libgtest-dev) do not provide pkg-config files, so you can build your own
-googletest using the steps below:
-
-```sh
-git clone https://github.com/google/googletest.git -b release-1.10.0
-cd googletest        # Main directory of the cloned repository.
-mkdir build          # Create a directory to hold the build output.
-cd build
-cmake ..             # Generate native build scripts for GoogleTest.
-sudo make install -DCMAKE_INSTALL_PREFIX=/usr
-
-# Optional steps if pkgconfig isn't installed to desired location
-# Modify the source (/usr/lib/x86_64-linux-gnu) and target (/usr/lib) based on
-# your local installation.
-for f in $(ls /usr/lib/x86_64-linux-gnu/pkgconfig/{gtest,gmock}*); do \
-  ln -sf $f /usr/lib/pkgconfig/$(basename $f);
-done
-```
-
 ### Rust dependencies
 
 **Note**: Handled by `--run-bootstrap` option.