AIX: Drop redundant -brtl flags

We removed `-brtl` in commit bce7a2a3a5 (AIX: Do not use -brtl to create
shared libraries, 2013-03-11, v2.8.11~103^2~1) but it was added again by
commit f254276fc1 (AIX,HP-UX: Fix RPATH handling when CMP0065 is set to
NEW, 2015-12-11, v3.4.2~4^2).  Since the latter commit we initialize the
`CMAKE_{SHARED,MODULE}_LINKER_FLAGS` to use the `-brtl` linker flag.
This is unnecessary because we already use the `-G` linker flag which
implies `-brtl`.

The latter commit also moved `-brtl` to `CMAKE_EXE_LINKER_FLAGS` from
flags that were always included in executable link lines with CMP0065
OLD behavior and are not part of the change intended by CMP0065.  Leave
this for now as we've always enabled runtime linking for executables
(and implicitly done so via -G for shared libraries and modules).

Issue: #13997
Issue: #19163

Modules/Platform/AIX-GNU.cmake

@@ -11,8 +11,6 @@ set(__AIX_COMPILER_GNU 1)
 #
 # By default, runtime linking is enabled. All shared objects specified on the command line
 # will be listed, even if there are no symbols referenced, in the output file.
-string(APPEND CMAKE_SHARED_LINKER_FLAGS_INIT " -Wl,-brtl")
-string(APPEND CMAKE_MODULE_LINKER_FLAGS_INIT " -Wl,-brtl")
 string(APPEND CMAKE_EXE_LINKER_FLAGS_INIT " -Wl,-brtl")
 
 

Modules/Platform/AIX-XL.cmake

@@ -11,8 +11,6 @@ set(__AIX_COMPILER_XL 1)
 #
 # By default, runtime linking is enabled. All shared objects specified on the command line
 # will be listed, even if there are no symbols referenced, in the output file.
-string(APPEND CMAKE_SHARED_LINKER_FLAGS_INIT " -Wl,-brtl")
-string(APPEND CMAKE_MODULE_LINKER_FLAGS_INIT " -Wl,-brtl")
 string(APPEND CMAKE_EXE_LINKER_FLAGS_INIT " -Wl,-brtl")