Partial revert of commit 7a100643.

If CMake doesn't support building libre2.a and libre2.so together and
installing them together, then it isn't suitable for use in packaging
and so installing re2.pc isn't needed.

Fixes #215.

Change-Id: I83e329f39da97ed6c4184564bd4ac85709800213
Reviewed-on: https://code-review.googlesource.com/c/re2/+/44630


Reviewed-by: Paul Wankadia <junyer@google.com>

CMakeLists.txt

@@ -147,10 +147,6 @@ set(RE2_HEADERS
     re2/stringpiece.h
     )
 
-set(includedir ${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_INCLUDEDIR})
-set(libdir     ${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR})
-configure_file(${CMAKE_CURRENT_SOURCE_DIR}/re2.pc ${CMAKE_CURRENT_BINARY_DIR}/re2.pc @ONLY)
-
 install(FILES ${RE2_HEADERS}
         DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/re2)
 install(TARGETS re2 EXPORT re2Config
@@ -160,5 +156,3 @@ install(TARGETS re2 EXPORT re2Config
         INCLUDES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
 install(EXPORT re2Config
         DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/re2 NAMESPACE re2::)
-install(FILES ${CMAKE_CURRENT_BINARY_DIR}/re2.pc
-        DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig)